The do charge for PSN. It's called PSN+ (does the plus symbol work on this website yet?). People who pay for plus get tangeable benefits, like cheaper PSN games, free games, earlier access to some content, exclusive access to other content.
As long as on PSN you can play online and shop online and get 3rd party paid for services (like Netflix) online for free then pretty much everything else could be rolled into PSN plus, including demos and betas, and I wouldn't really care.
With online pass, publishers (incl Sony) have an additional revenue stream for keeping online play free to new game buyers, so there's really no need to make online multiplayer/coop a paid for service.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
