Importance. Microsoft (rightly) considers smartphones to be a serious, if not existential, threat to them, breaking their near hegemony on personal computers. Given the importance, Microsoft should be willing to throw vast quantities of resources at WP7, to save themselves.
In fact, the same arguement as been made regarding G+: Google sees Facebook as an existential threat, so they'll throw money, time and engineers at it until it works (or falls so flat that there is no chance whatsoever).
In fact, the same arguement as been made regarding G+: Google sees Facebook as an existential threat, so they'll throw money, time and engineers at it until it works (or falls so flat that there is no chance whatsoever).