•WP7 uses C#, and C# compiles practically instantly, making for more rapid iteration times. Objective-C and C++ compile very slowly by comparison.
•Visual Studio's debugger is unmatched in performance, features, and stability. XCode's is an unstable, slow thing built on top of the arcane gdb.
•WP7 games are based on a framework called XNA that Microsoft includes. XNA takes care of a lot of the low-level headaches of graphics, audio, and input processing. On iOS, you have to write a bunch of (relatively) low-level code to get anything working.
-- Mike Dussault
If there's one thing that Microsoft should be proud of in their attempt to compete with iOS and Android, it's their fiercely loyal community of Windows Phone developers. Why do they have such a strong community? Probably because they gave them great tools. See some more advantages that Dussault mentions in the article link below.