that one year accounts for millions of sales, a bigger userbase, which gives devs more incentive to develop for that console, which accounts for more games, which accounts for even more sales.
now that 360 is in that position, with the highest userbase, the most games, good games, and more incentive for devs to develop for it. not to mention its a lot easier to develop for.
even konami is trying to force metal gear to the 360.