Err, numerous exclusives, Sony spending millions to get FFVII on their console, MS giving Halo 3 beta passes for those who buy Crackdown, MS securing exclusives for its console and spending money for the marketing, Sony making its online service more open to third parties, Sony and MS sending programmers over to Rockstar to help them with GTAIV, etc. Yeah I can name a LOT of examples.
The Wii sold a lot because it came out cheap during a generation-transition phase where new consoles were/are expensive and few games were being released. In one year from now you can be sure it will settle for good in third place.