Well I bargain shop for games, so that's why I have so many unfinished. I wouldn't have purchased my newest three had Gamestop not had a sale going on. Sometimes it's better to buy before you need it if it'll save you some serious cash. Others I just buy on day one because I have the urge that I need to play them immediately. It causes the conflict. Luckily Spring is looking rather empty outside of maybe five games, so it'll be good time to play catchup no matter the route I go. I only have Wii Sports Resort, MadWorld, Street Fighter IV, Res Evil 5 and Killzone 2(if I go for a PS3) to get.
Well, at the heart of it is this:
You will never be able to play all the 360 and Wii games you would like. Purchasing them just makes the most sense. I always go for the option with the most games, myself.