The whole thing comes to one point in the timeline:
when the Galaxy S and iPhone 4 were released.

For Nokia to be competitive today, they needed to have the N8 (Belle) and N9 (Harmattan) selling back then, which is Q4 2010.
or...
They needed the Lumia 900 with Mango.

Honestly I can say the WP is a better ecosystem, but MeeGo is a better OperatingSystem. With OVI (carrier billing) and NOKIA, MeeGo would've even surpassed the ecosystem that MS holds (Zune, Live, Skype, Xbox-Persona Integration). They just didn't play their strengths and became susceptible to their weaknesses, and all-in-all didn't release an innovation in the correct time (18 months too late).