3rd parties are followers, not leaders. They will develop games for ANYONE who can provide them an audience. They don't much care whether Sony, MS or Nintendo wins, so long as they have an outlet to sell games. It is up to the console manufacturer to sell their system to the consumer,and sell enough of them to make it worth while to 3Ps to make games for that system. Fail to do that, and the 3Ps will jump ship, and drive away any potential market for that system.
Two things to consider:
1)Nintendo has had little third party support for 2 generations. They alienated 3Ps with the N64, and, despite significant efforts to repair their relationships, couldn't sell enough GameCubes to keep them on board. No question then that the Wii launched with the weakest 3P support of any current system, and yet it is selling like gangbusters. Now the 3Ps are scrambling to catch up.
2) At launch Sega's Dreamcast arguably had the best 3P support of any system interms of both quality and quantity, and the system ended up a stunning failure.
Think of third parties as a weather vane. They don't make the wind,but they do tell you which way it's blowing.
