For many Nokia are Windows Phones. All the other companies just do WP on the side with Android as the main focus. If Nokia goes under (by that I mean gets bailed out by Microsoft/sold/etc.) it sends a HUGE message to developers that this platform isn't worth putting resources into. Not that many are at the moment anyway.
And that's the main problem. Apps. Not that I care about them but Draw Something, Angry Birds Space & Instagram aren't available for WP. That's enough to put off the vast majority of people. The core of Facebook is well supported (with OS integration) but the app is awful and the mobile touch website doesn't work properly in IE. Official Twitter app sucks. Skype sucks. I could keep going on.
My Lumia 710 is good. The OS is good. The apps though are severely lacking and for most a smartphone is about the apps.