But both Live, and especially Steam are extremely successful. Both Steam and PSN are free to use, unify players through a unified community, and generally make it easy for both the consumer and publisher to benefit from each setup. If you leave it all to individual publisher, I imagine it would be more frustrating/confusing for the consumer to have to handle various networks, especially if some of those choose to make the consumer pay. (which I doubt would happen, but hey, activision, etc etc.)
Like you said, I guess we'll have to see. I'm interested in this other idea, but so far I don't see much reason for it other than just going a different route. Avoiding something because a competitor does it one way, doesn't mean they can't be successful doing their own, and I think most their consumers would welcome it.