Do we really need a deep conspiracy theory angle to explain the deprecation of a horribly lagging OS (Symbian) and a next-gen OS whose development was severely lagging even behind WP7? The board brought on Elop to do precisely what he did - any ire should be directed squarely at them. Say what you will about RIMM, at least they aren't striking at the prospect of QNX replacing their OS.
It looks like even the previous gen (Maemo) of the next gen (MeeGo) has sold better than WP7
WP7 hasn't been a runaway success, but at least it's stable, polished and backed by fairly advanced web services. The bet is essentially that Nokia's 1st rate supply chain combined with a polished new OS can sell more than either could have otherwise.