Noted at http://www.codeproject.com/Articles/366275/Windows-Phone-WinRT-why
Don't be surprised as developers take notice. Again, 3rd Party folk are not welcome.
It appears MSFT is locking down the system and anyone that they don't want from the platforms.
Windows Phone OS is now officially part of the major league, folks. The Marketplace for Microsoft's mobile OS has made it past the mark of 100,000 application submissions, thus joining the likes of Android and iOS as part of the elite club.It took the platform the relatively short 20 months to reach the magic number - that's quicker than Android (24 months), but slower than iOS (16 months).
Out of the 100,000+ submitted apps, 88,371 are available for download across 60 countries. That number is bound to increase with around 300 every day. Don't be surprised however, if the pace picks up even further - after all, Windows Phone Apollo is right around the corner.