So for that reason they decided to go into the rich Windows Mobile ecosystem? What kind of installed base is there for Windows Mobile nowadays? 5.7% and falling steadily.
Sorry but if the richness of the ecosystem is the main reason for change, then the obvious answer is Android.
Multiple reasons imho: They got a great deal from Microsoft that Google wasn't willing to match, the OS is beautiful, plenty of existing Xaml developers, great platform + language and better tooling than Android or iOS.
Everyone is under the impression that the waters are poisoned or they'd be flocking to the platform.
XNA is actually a decent toolkit, and the Visual Studio environment is way better than the Android Eclipse mish-mash.
What's preventing uptake is a complete lack of understanding in their market, an inability to take down even weak competition like RIM, and no clue how to leverage their success from the 360 on to a phone.
If they'd just called it the Xbox Phone it would've sold ten times better.
To a degree Apple is a poisoned brand. "Everyone" thinks their products are way more expensive than the alternative. It's a mindset they've had to work to undo.
Even as an Apple fan, I always thought the 8-core Mac Pro was expensive compared to the alternatives, yet the Dell equivalent is about $800 more.
Sorry but if the richness of the ecosystem is the main reason for change, then the obvious answer is Android.