maybe u have to think at the problem less deeply, and just see that nokia lost the train.
as long as the other devices, and after android got a lot of updates, programs, games, nokia did not do anything. for about 2 years no other great devices, or something else. they waited too much with this WP thing, but, probably, if they stay can wait enough, and prove themself as serious, with a lot of support for the devices they sell ( not as for n900 ), probably they will manage to take some of the market.

from my point of view is just a matter of timing and os maturity. wp is at the begining, did not proved that deserved to be bought, but, at least theorethically would have a great pothential, which is not demonstrated yet.