Just having a marketplace for your smart phone isn't enough of a selling point. Smart phone makers must demonstrate web application developer interest--as community contribution is vital to the survivability of any competitive smart phone.
A business plan built upon outsider developer creations is not typical of the Microsoft approach. Microsoft recently announced that it has hit the ground running with 15,000 developers. Currently, Windows Phone 7 has 3,000 apps available. This is truly a good sign for the software giant, which has not, to this point, had much success in the mobile market. Windows Phone 7 has a lot of catching up to do with Android and iPhone. Android currently has 100,000 apps and the iPhone has over 300,000.