Thing is, a lot of people are net savvy and register to websites with false details (DOB, addy etc) - but lots of people don't...
But I do think that even if you are surfing on one site anonymously, there are agreements and methods that the General Public don't know about that can identify you unless you use anonymous proxies via unregulated countries. Who goes to that length?
I don't think that any law force could be arsed to trace down Mr Smith for calling A Stealer a "cheating bastard" on Some Portal, but I think that A Stealer will be well inclined to hassle Some Portal to make sure it regulates its users.
This forum is good, with good people, although some may bitch it is not tecnical enough (there is plenty, and there are more sites that do techie stuff) - my humble opinion is that this site is a community and therefore self policing with great mods - I can't remember the last crap post I read (no jokes), compared to other sites when you have to surf through loads of crap and slander to find measly morsels and tidbits.
my 2p! I'll shut up now