> Having to create a separate account on N services with the same credentials is simpler than having a unified account?
I said it wasn't complicated, that's not the same thing as saying it's simpler.
What's simpler is going to depend to a high degree on your use of the system.
For instance, I do some work with disadvantaged people - charity/volunteer stuff - and some of the people who haven't touched a computer before cannot understand that the government won't be able to track them through their Universal Jobmatch accounts if they use other websites that don't use that sign on. For them, it probably is simpler to have one log on.
Taking myself as another example though, I'm obviously going to find it more complicated to manage alternate identities, that have to at least passingly sound real, to ensure my privacy than I did just not having my real name online at all and reusing some of the assorted user-names I used on other sites while using different email addresses to stop it all getting tied together.
It's a trade off - at least from a user perspective - what are you optimising for?
As I see it, you gain some small ease of understanding for people who have just never used a computer before, (and increase the penalty when they mess up and leave themselves signed in on a public computer, which they do .) And you get some small benefit if you want to change your email address across all the service (though how often does that happen - and how many services do you really use?) However, you make it more difficult for people to remain anonymous.
There's also the fact that a similar thing could have been done without tying everything through G+. Which of course they're not going to do because they want to force you to use it.
We're talking about marginal gains, in return for making things much harder for those of us who don't want our names floating about associated with all we do.
(That and I question whether it's a good idea to make people have one sign in for so many things anyway. Nanny-state-me is like 'That's a terrible idea, the only thing worse than a crap password is the same crap password for everything.' )