Thing is, only one of your offered reasons was anything of an opinion (the UI). Development environment I know is good, to debate that is retarded (wholly missing APIs is brutal however, which will and is causing the same situation WebOS faced).
Zune Pass is no longer relevant (and this is coming from someone who was a diehard Zune Pass fan. In fact, I too specifically looked forward to WP7 for that reason.). There's better services out there that do streaming combined with offline storage/caching. Grooveshark is one example, with a much larger library, cheaper price, works on Mac, works via the web, and most mobile phones.
As for control/fragmentation, there's a LOT of downsides to this. MicroSD cards that can't be removed, no USB storage support, most devices are identical, and there's so far very little indication about carriers not getting their way with the platform.
Wookie: Beware, there's almost no Google integration allowed. In fact, Bing search is mandatory across the device as far as integrated services goes.
Microsoft actually pushed really hard before release for development of apps. There's no reason they couldn't have done even more in that area (contests/straight up payments/etc).