There's been some other commentary floating around on this as well -

Joystiq, Blackguard, and Raph all have their piece to say on it.

The researchers in question are long time gamers and have invested a lot of time and passion into the MMO genre, so it isn't as though this is something that a couple of egg heads simply stumbled upon. Personally I'm with Raph on this, while not a revolutionary statement by any means it now gives us a formalized scientific study to point to that extols the virtues of Virtual World/MMO spaces as places of social worth.