I admit such a number be highly variable to the individual. But if I were wagering, I would peg it somewhere around that percentage. (Though I don't do well at gambling, so there is that.)
I wonder if media consumption is like counting calories. They do say that (due to various factors) it is impossible for consumers to do so accurately.
Interestingly, can you truly know if my post is commercial in origin. Maybe I am some kind of covert influencer, paid to sow any number of memetic seeds. (Perhaps I'm not even a person as such, at least, not a flesh and blood one, but merely a rather limited Markov Generator.)
(Though, it isn't---at least, not the first part---I'm very much not getting paid money for this.) Which is not to say, however, that I am not getting paid. That is to say, without these posts, I don't exist in this environment. My post, like yours and everyone else's here, is our ongoing construction of both the accounts which contain our social assets (assets that extend even beyond this realm) as well as the social assets themselves, that is our identities in our own minds, and each variant of that identity that exists within each reader of each post we submit. (Facebook highlight reals, various forms of virtual signaling in the comment section for news articles, etc would fall into this category. Though, in a way, this in an interesting model for post-capitalist future, in that, baring those who are an such services for business promotion, Facebook, Twitter, etc are all commercial endeavors where users churn-up content for no commercial compensation, ultimately ultimately creating the state in which these entities can acrue capital. And even though it doesn't in the same way as those entities, HN itself (and the social reputations generated on it) are deeply intertwined with combinator as a whole.) But those identities are also backed by copyright, interestedly enough. And I would claim your ownership of this identity (at least so far as it can be owned, that is the specifics of each post) is intrinsic, no matter to what degree you decry copyright. For example, without such, you collective posts could be taken by anyone and edited in any fashion they desired, thus crafting any public version of you they wanted. It might be argued that if keep libel and defemation laws around, that that wouldn't happen, but doesn't that just become a kind of backdoor copyright? A so-called creator could claim that no matter how the work were modified it would be prejudicial against them and that, even, perhaps, that distributing it to unapproved entities would be also be so (though, that likely is stretch).
Also, I think that there is a disparity in, shall we say, length. That is to say, users are, in general, willing to trade effort that raises capital for an entity wholly other for themselves, in exchange for the opportunity for the construction and maintenance of social capital. And we can see that as a fairly textbook value transaction. The question is how far it can be pushed. The rights already granted to entities such as Facebook would, I would argue, if they tried to pursue it, that the user agreements of such entities grant enough leeway for them to employ a large portion of their generated content anyway they wanted, not just the re-serving of it and the cataloging of it. So let's imagine they do so, using such data for say, effectively, crowdsourced filmmaking, or some such. At what point would the user base become dissatisfied with this? That is, at what point does the value of the transaction shift? So the overall question becomes, while users are willing to generate, in exchange for a certain amount of social capital, a few memes and one-liners, and the typical length of a post on HN, are they willing to do so for substantial work (that is to say, would the typical user be willing to give Facebook one or more 80,000 100,000, 200,000 word books with all the result capital flowing, then, to that entity?). And we can extend this to full-length film, etc. Would anyone even want to create a three-minute music video under such circumstances? (And I don't mean this question facetiously.)
I do know those who create (16-bit game assets, for example) and release those creations under the terms of CC0, being as close to public domain as possible, though don't even think that is close enough, but I still can't help from wondering how they would feel if those works were consistently used in multi-billion dollar grossing games without even mention of their name (unless we are going to retain moral rights from copyright, that is). Considering the actual reactions of many people when they found out their creative commons material was used by corporations, rather than purely 'the community', it does lead me to believe that people aren't thinking of even these licenses (again, all of them backed explicitly and only possible because of copyright) in terms of the whole of the world, the actual world.
What we have to keep in mind about the post-copyright world is that it doesn't start from zero. Every media company that exist today, will still exist with their accrued capital in the post-copyright tomorrow. To be sure, they would take many hits (and I would not say otherwise), but just in size alone they will continue over every solitary self-publisher.
And I do not doubt that people will make things. It is the things that they do make that I do question. In such a world where only the actual of social capital could exist (an impossibility, I obviously state, at least under any circumstances the human race has ever known) it might tend towards mass appeal, but even then, why would anyone go wide (except in the case of the most megalomaniacal) when instead they could concentrate their efforts on fewer and more likely targets of localized social acceptance? But, to be honest, I don't know if that question could even be answered. But the more concrete question, at least in my view, is: if all the so-called creator gains in the social capital aspect (and even that is up for question, as if Disney makes a version of it, everyone will know it from Disney), but that is all the so-called creator gains, and they repeatedly watch as others raise themselves within the social order capital accrued from being based on these works and their own social capital accrued from the wider distribution of the works (remember the reaches and assets of those established companies will be larger), repeatedly watching this transference, how long are such individuals going to last? And I will repeat that I cannot see any rational person doing so (or at least what we call rational). So it remains for (except for the few exceptions that will most likely arise in any system (as do the Stephen Kings and J K Rowlings in this one) and those workers who would operate within, perhaps, my previously imaged theatre system, though even they might not amount to much, merely stitching together garments from pre-existing public domain properties based on the tastes of the audience, or maybe even replaced altogether my sufficiently advanced Markov Generators (there's already one that can write passages from 50 Shades of Gray)), so it rests with either the insane or the driven (and driven here has to refer to artistry driven, the ones most likely to create so-called 'weird' stuff, simply for the fact that being a commercial entity and doing things that aren't 'hip' weird, is the road to obscurity or penury, though not necessarily without critical acclaim, but one eat critical acclaim unless that social reputation can be traded in on (ala, we get a lot of creative writing instructors).
(But, of course, that is only my view from my experiences within the related communities.)
*edit communities, not communists