I think some of both. Many sites that accept comments now encourage commenters to log in with their facebook accounts, so that can be a major factor. I hve not seen it yet, but I suspect something similar will happen as G+ leaves beta and becomes more established with it.
Also, as I have read in other commenters, a social network is only valuable if your friends are on it, so while alternatives exist it may be hard to find the people you need to find on them.
I agree that Google+ will probably get in on some sort of "Login with Google+" thing.
I guess someone could see this as this real name policy then "infecting" the Internet. It would really come down to why are these sites implementing this service. If they are doing it for ease of use, so the user doesn't have to create another account, and there are no alternatives that don't require you to use your real name then that could be bad.
But if these sites also want people to use their real names because they feel it would foster a greater sense of community then that is their prerogative.
There is no one service yet that rules over the Internet and so there will always be alternatives. If a service requires you to use your real name then you can just choose not to use it.
I'd grow more concerned if governments and ISPs attempted to implement a "driver's license" for the Internet. Personally I wouldn't mind this but a lot of people obviously would.
Also, as I have read in other commenters, a social network is only valuable if your friends are on it, so while alternatives exist it may be hard to find the people you need to find on them.