I'm generally enthusiastic about the stuff I like, and consoles are no different. Whether it's movies (go watch TDK, now) or games or whatever, it's nice to have other people into the same stuff. As to why, I'm not sure - perhaps a combination of it affirming my opinion is correct, and being able to talk endlessly about it. While the 360 isn't my favorite console, if I can get somebody that isn't into gaming interested with the 360, I'd be glad to. Same for Wii Music - heck, one main reason I'm buying the game is to suck some non-gamers into my world 
Funny you bring this up, as I am sort of in the process of "converting" a user living in a PS1/PS2-only home onto Nintendo's side, and I'm a bit fanatic about it, lol... It actually isn't unreasonable though, since the games the person is into (jRPGs, casual stuff) is always strongest on the market leader. The person doesn't keep up with gaming news, so it's pretty much my job to inform em of what's going on, and telling them about Sony losing the lead comes off as a surprise. I admit it does make me happier when I'm able to recommend something I'm more a fan of, though.
