This is based on what? You can't write apps in a language both WP7.8 and WP8 understand? I understand MS introduced new options for languages, which I assume e.g. big game companies will make use of, but those little apps, which make up the vast majority of the market, I tend to think will be written as now also in the near future. So perhaps in a few years the balance will tip, but then I guess it's time to upgrade anyway. Not that I know anything about software development. Also, didn't Nokia do this very same thing with Symbian and Maemo quite a few times? Except Nokia did it worse. N900 can't run N9 apps, and vice versa. At least WP8 devices can run WP7.5 apps, which I think is quite good indicator that it will not be difficult to write apps for both versions (as long as those apps don't specifically make us of the hardware enhancements)..