There hasn’t been an official WP7 device yet, the developers are already interested in developing for Nokia-Microsoft. The 29% qualifies for 5th place with iOS first. There is a major battle within Windows 7 OS and Blackberry as Blackberry comes after Windows.
Symbian is heavily falling behind at second last place, Nokia pans to launch more Symbian devices this year. These responses are only based on 2670 developers, some which may not want to develop at all.