No game is ever a savior. The term is completly misplaced.
Wii Sports help lead the Wii to #1. Gears of War helped the 360 take an early lead and gain real momentum. Neither game was necessary for the success of the console, though. It takes a lot of games...
Monster Hunter helps sales but isn't changing the overall view of the PSP much.
No one game can sell a console, though. The PS3 has a ton of great games and will just continue to get them.