They don't get instant access, though. As a developer I already have to support both Google's flavor of Android and Amazon's flavor of Android, with their own

They don't get instant access, though. As a developer I already have to support both Google's flavor of Android and Amazon's flavor of Android, with their own separate implementations of IAP, push notifications, etc. I'd have to support MSFT's implementations too and you'd have to convince me (and the people who pay me) that it's worth bothering to do.