Microsoft can't build the kind of developer community that Google and Apple have. The interface is smooth, and the Zune Pass is great, but there has to be more.
Can't build? Why not? Developers in general love their tools (Visual Studio), the language has a huge user base (C#), and they're leveraging a rapidly maturing framework (Silverlight).
If anything, when it comes to getting developer mindshare, it seems like Microsoft has a huge leg up.
Microsoft is the development platform of choice for big business. The hottest startup to use their stack in recent memory is StackOverflow. Generally speaking hackers choose not to use Microsoft's platform when they have a choice. Personally I use c# at my day job, but I barely considered building something for the WP7, and am instead working on iPhone and Android.
