Your assumption is only true if the user experience stays the same. Some things (like web mail) take off even when the user experience sucks, but other things that people actually want can be held back by poor user experience. For an example that has spanned practically the entire history of the internet, consider online gaming. The first internet gamers (MUDers? my history is weak) were a small population of hardcore geeks, but as the user experiences got better, the number of people playing rose in a kind of slow-motion explosion. When each breakthrough game appeared, it attracted a new crowd of players who until then had not found online game slick and engaging enough.
In 1985, 1990, 1995, or 2000 you would not have extrapolated the current percentage of online users playing social games into the future, because it was obvious the experience was going to get better. It was easy to imagine better graphics, sound, responsiveness, and social interaction, and everyone assumed the better experience would attract a broader range of users.
With RSS it's not so easy to imagine how the user experience will improve. We're suffering a failure of imagination. We have the use case: Checking for recent updates on a web site is something people do all the time. They even do it on web sites they're visiting for the first time, and it can be really frustrating depending on the organization of the web site. We have the technology to serve this use case: RSS.
So the users want the information and the browser can get it. We can't yet imagine an effective way to present the information to the users, but proof by failure of imagination is no proof at all. Personally, I think it's likely that someone will find a graceful way to present RSS information to the user, and RSS will disappear from our sight and from our vocabularies into a heretofore-unenvisaged UI element.