A question “are Microsoft’s own applications on Windows Phone 7 Series based on the same development platform it exposes to third parties, Silverlight?” was raised. The short answer is “NO,” reason “default” apps aren’t built on Silverlight is actually a technical problem, the apps were simultaneously developed with the platform and tools when they committed to building the OS from scratch. Having said that, neither users or developers should be concerned as Microsoft assures this’ll be no disadvantage to third parties. In terms of performance, they state there’s no discernible difference in processing or rendering speed of 3rd-party apps. On other hand, breadth of APIs could’ve some differences but developers of other smartphone platforms like iPhone face this too. Microsoft vows to surface additional APIs if developers voiced their needs. Microsoft wasn’t able to confirm or deny the use of the “Iris” or UIX framework, but references to UIX in the ROM dump would strongly suggest so.