Killing off Symbian in a speech while shipping more phones than any company on earth was, generously, not part of any strategy but a horrific blunder, less generously, it was sabotage. I've got no love for Symbian, but when you're selling that many phones, you phase it out, you don't announce to the world that there's no reason to buy the phones you're still trying to sell.

Porting Symbian UI to Qt meant that they could at least merge surface-level stuff and have core apps that ran on both Maemo/Meego and Symbian, then retire Symbian when no one would care or notice.