I wouldn't underestimate the huge number of .Net / Windows developers that exist for Microsoft's ecosystem. If they manage to line their technologies up just right and make a big push for the mobile space, there's a huge developer mindshare that's entrenched in the Visual Studio / .Net world. A lot of these people have never used a Mac or other OS, and never programmed for another platform. Many of them don't have the interest to switch over to Java or ObjC and would prefer to work in the MS ecosystem. These are the people who would be developing the apps.
If a developer's personal inertia / sloth around learning a new framework is such a factor that they'll choose to develop for W7 rather than iPhone or Android, that doesn't bode well for the quality of the app they're going to produce. Most great devs I've ever worked with are perfectly happy jumping languages / frameworks if it means their work will be more successful.
