I'll buy consoles for one game if I want to play the game badly enough. In fact, I think I originally bought most of my systems for one game. Usually I find more games that I like eventually.

Gameboy Color: bought for Pokemon Blue
N64: bought for Pokemon Stadium
PS2: bought for DDR games
DS: was an impulse purchase on my birthday because I wanted to play Animal Crossing
Wii: bought for Twilight Princess
3DS: bought for Ocarina of Time 3D