Brand loyalty, plain and simple. When I got my Wii, the only game that I bought for it was Resident Evil 4 (which I'd already played to death on the Gamecube). If it were any other console manufacturer, I'd probably have waited for some must-have software.
It was a good purchase, no doubt. Still, if I said anything besides brand loyalty, I'd be lying to myself. I don't lie to myself......unless I'm talking about my massive penis.