I suspect the overall decrease is because the growth of Windows Phone isn't as strong as the decline of Windows Mobile.
Overall I think it would have been a good idea if Microsoft had done better in separating the brands. Right now its to confusing for the average user if reporters can't get it right.
> The only way to be sure would be to see sales numbers from Microsoft. The fact that Microsoft hides those numbers is telling.
Or we could look at the size of the market at times when we know the percentage of the market they have, which gives us absolute numbers, and then graph those over time.
Calculating from that, Microsoft has plummeted from 3,041M units to 1,724M units. In other words, Microsoft is now shipping almost half the number of phones it was shipping last year.
That's much worse than I had imagined.
Another datapoint, Bada has doubled in marketshare and now exceeds that of Microsoft.
My guess is that it is shrinking, not growing.
The only way to be sure would be to see sales numbers from Microsoft. The fact that Microsoft hides those numbers is telling.