Not everyone decides to skip sleep. Lacrosse may (usually) be better for you physically (assuming you don't get injured. it's hard to get railed in the face playing WoW), but I don't think that you can argue WoW is largely a social network. You meet more people from around the world.
If it's the "social network" you're after, why not join a global chatroom, Facebook, etc? Most likely the friendships you make on WoW are going to be without substance, whereas in lacrosse the friendships I make are with real people who I actually know.
Well, I'm going to say that, seeing as WoW is a computer game and it's something that I enjoy, it's more likely that people that share the same interests are going to be playing it. Not necessarily, just more probability. As for Facebook, chatrooms, and myspace, and anything else associated with them, I've pretty much blacklisted them for being drama traps.
WoW is suited for people who enjoy playing it, and sports are suited for people who enjoy playing them. I don't enjoy throwing around balls, so I don't associate myself with people that do.
(And, relationships through WoW aren't without substance. A lot of the people I play WoW with are people I've known for several years and have come to respect, and some even wanting to get together. Hell, one of my guildies from New Zealand has the money to come visit me and may do so at some point. I think in some ways these relationships do have substances because they are so able to thrive in such a long-distance environment. That's my opinion, though. Which is why I played WoW, and you do not. If everyone felt this way, then Blizzard would own the galaxy.)
