They do have an incentive.
Windows 8 is just the beginning. It will be locked down and taxes levied on anyone still inside. Everyone knows what microsoft is planning to do, and their little threats to Sony players prove that. They want to play the monopoly card to try to get their way.
So that will cut into everyone's profits. Publishers like EA created origin to RUN from fees. Now microsoft is trying to muscle everyone out through their monopoly and the creation of a windows store.
And since Direct X is used as a weapon now , and locked behind certain OSes that NO ONE is using or wants, it gives them all the more reason to drop Microsoft. Windows 8 is a flop, and their insistence to continue down that route is killing PC.
Everything microsoft ever did was a headache for everyone else. There is a reason microsoft is seen as hitler to the mainstream population.
AMD and Nvidia know whats coming. Steam, publishers, and every dev knows whats coming. Even Sony benefits from helping drop Direct X because that's less leverage Microsoft has.
This has been a long time coming. Everyone has a reason to drop Direct X because of Microsoft's bullshit. Especially if they start locking everything down.
Origin won't exist.
Uplay won't exist.
Steam won't exist.
Neither will GOG, Green Man Gaming, Gamefly, and everything else. Only the windows store will exist. The publishers will have to pay whatever MS charges. No negotiations.
Even if they hated steam, they know that MS is worse.
The only thing that's stopping Linux from taking over is a lack of tools which valve and other devs are looking into now. Its free, and no one can tax anyone else for it.