Do they not use it as a selling point? If so, than I'd say yes they are obligated to give it. It's like buying a happy meal and they tell you it comes with a toy and then when you get the toy (after you pay) they say "you can only use the toy if you do something for us" Gimmie My F^^king Toy!
That is how services work, even if it is a selling point, you still have to agree to terms before using it.
You can't compare a one time thing with something that you use over time. What do you say to the guy who been playing on-line since the ps3 first came out (5 years ago)? At first they say, hey buy it you can play on-line. Now their saying you can play on-line only if you agree with us. That person should be able to return it than because it isn't what he agreed to in the first place.
Actually, they said you can only play if you agree with us way back when they first started playing online when they agreed to the original ToS. And part of that ToS is that they can terminate the service at any time for any reason, and not agreeing to the new ToS is a perfectly valid reason to terminate the service.
Again, your rights are not being given up, your right is the option to choose to agree or not. People need to learn that the consiquences of their chooses aren't violations of their rights.
But how many of the other ToSes have changed? If it was like that from the beginning than OK the person has no right to bitch, but they are changing it. They are still legally bound to the first ToS. I guess you are looking at it from a U.S. point of view. Thankfully, most of the rest of the world sees it differently.
Even the places that are seeing it differently, the original ToS is invalid. There is no modern country that forces a company to continue to provide a service when the original ToS specifically says they can terminate it at any time, and that is what the original ToS says. So if they don't agree to the new ToS, they don't get the service, end of story. The service provided by the original ToS is terminated either way, and Sony has every right to do that.
Nothing new, the legallity of giving up your option to sue collectively isn't at question here. Sony has already covered that because it says in the new ToS that local laws might not allow someone to give up their option to sue collectively. That isn't at issue here, in locals that don't allow this that section of the ToS doesn't apply anyway, there are states in the US that are like this as well.
However, Sony requiring your to agree to a new ToS before you continue to use PSN is perfectly legal and allowable anywhere.