I agree with most of what you said, except that Nokia taking the Windows Phone strategy and keeping it mouth shut would've killed Windows Phone before they could even ship a phone.
Which makes the decision to go Windows Phone (and kill the company in the process) even more intriguing.
That's quite possible, and that's part of why I would have probably gone with Android instead. Windows Phone is a really interesting OS, but Android -- even if you couldn't use the official Google branding -- gives you access to a much bigger ecosystem than WP's and a more vibrant one than Symbian/MeeGo's, while porting Qt would have let them keep the existing development community from feeling torched while also likely letting them bring along their new MeeGo UI, which was actually pretty cool.
I think Elop placed a very high -- possibly too high -- value on having a "partner" in whoever made their new OS. Microsoft was willing to be a partner on Nokia's terms because Microsoft was desperate; Google wasn't.
Which makes the decision to go Windows Phone (and kill the company in the process) even more intriguing.