I could go deeper, but let's put it this way. Harmattan is a version 1 rewrite/release that will probably not get any updated due to Nokia's CEO. WP7 is a version 1 rewrite/release that will get updates due to Microsoft's CEO - and Nokia. Too bad Harmattan will not get the chance it needs to mature.
The rest of your argument - Qt, et al - how many Qt devs are there out there versus Java, C/C++ and even Visual Studio developers?