Could you expand on the differences you see? Is it API-wise? (I'd expect WP7 tooling to be better than iOS's, though I have not yet had the occasion to try Xcode 4 I kind-of doubt it leapfrogged VS2010, except on the UI side maybe where IB and bundles have always been pretty nice) Is it the communities/help around them? Third-party resources? Something else?

And which ecosystem did you come from before iOS and WP7?

(disclaimer: I'm not a Windows or WP7 dev, and I only dabbled a bit in iOS dev)