As others have said, when a third party places an exclusive game on a console with a small install base, it's usually due to some kind of behind-the-scenes deal. MrPickles gave some good examples from the last generation; Microsoft paid a lot of money to get third parties to put games on the XBox. (This is one of many reasons why the console was a sales success, but a financial disaster.)
Nor is Nintendo above this sort of action either. The Gamecube only received the Resident Evil series because Nintendo wrote Capcom a big fat check. Final Fantasy: Crystal Chronicles has an even more interesting story behind it. Square wanted to port their old Final Fantasy games over to the hugely successful Gameboy Advance, but Nintendo refused unless Square developed at least one new game for their faltering Gamecube console. Square agreed, and that's how Crystal Chronicles was born. I know the series has its fans, but I'd argue that it's subpar status is due to how it was conceived: Square turned in a half-assed performance because they were only interested in re-releasing their old games on handhelds.
End of 2008 totals: Wii 42m, 360 24m, PS3 18.5m (made Jan. 4, 2008)
