Nokia’s CEO, Elop had stated that Windows Phone was a better platform for Nokia’s future.
It is hard to imagine how that is true versus the likes of Android, MeeGo, or even their own Symbian platform(which had begun to undergo changes that were starting to turn the tide for the platform).
With Windows Phone Nokia gets a platform they can influence and even slighty alter, but they lose the Qt development ecosystem that they spent the last year building up and possibly their developer user base with it. They also lose having full control of their ecosystem from OS to application services.