IMO the comparison between these platforms is only interesting when you take alternate languages into account. We know Java, C#, and Objective C are all way behind, so how do more advanced languages fare on these platforms?
For example, there are a few people running F# on Windows Phone 7. I haven't tried it myself, but here is a link to templates for game development with F# on WP7: http://sharp-gamedev.blogspot.com/2010/12/project-templates-...
Here's an article on building a WP7 app with IronRuby: http://msdn.microsoft.com/en-us/magazine/ff960707.aspx While this isn't as fast as it could be, because you can't access Reflection.Emit to JIT method bodies to native code, it does show you can run Ruby in a WP7 app.
Behind what?
Anyways... I can attest to F# being a breeze to get on WP7 and Scala can be wedged into android with some effort. Thats about it I think of in terms of no extra runtime required solutions.