Regardless of everyone disappointments, if Windows Mobile 7 attract developers, because let's say there's no dreaded App Review process,
Then, the amount of competition in App Store will decrease, hence it will give more time for Apple to fix things, create a better review process, and nurture the existing developers already established in the iPhone OS platform.
Developers' migration to Windows Mobile 7, may not influence Apple that much, because the existing customers for iPhone apps are still there. These customers do not worry as much as developers.
Everything will balance itself out.
The best platform in the "eye of the consumers" will still wins, instead of the best platform in the "eye of the developers"