You make some good points, but you have not convinced me that Nokia's downfall was totally unrelated to their open-source strategy. Of course, I would not be surprised that there were also other factors at work, but from what I can see, their approach to open source was a contributing factor.
Then again, there is a good chance that Nokia's current experience will become a prominent business-school case study. In which case, few will pay attention to what either you or I think about the matter. ;-)