The Danger acquisition didn't really make sense from an engineering perspective - the Sidekick was a great phone - 5 years ago.
MS doesn't have the greatest track record with consumer products (Xbox not withstanding).
They OWN the enterprise. While I'm not sure the resulting products would be all that great (though everyone usually has great things to say about Windows 7 Mobile), it would be an easy sell to an enterprise.
Chinks in the apple/android armor:
1) Right now, enterprise applications have to go through the App Store (for both devices). It would be pretty powerful for enterprise to be able to push their own applications at their leisure to their phones
2) Existing tie-in to blackberry servers.
3) Android phones irritate me b/c you need a gmail address to even set it up. This is just an additional requirement for enterprise phones that shouldn't even be there.
4) Dev tools that people are familiar with. Objective C experience is harder to find that C#/.NET experience (Android is wash here with Java).