Firstly, This is opinion, not fact. It isn't born out by the current global figures. All the major stat counters (StatCounter, Net Application, W3 Counter, Clicky etc) show IE being ahead globally. Yes, there are regional variations and yes IE's market share has dropped over the years, but that does not support your above contention.

Secondly, the version of IE on Windows Phone 7 is actually IE Mobile 9, which is not the same thing as desktop IE9 (just as the Mozilla-based MicroB on the N900 is not the same thing as Mozilla Firefox); they could just as easily called it Fred.