No, I didn't forget. Again this is speculative theoretical nonsense. WP7.X users will be the majority for a long time. New apps will be written for WP7 and can also run on WP8. Gradually as the WP8 user base increases, the most advanced apps will run on WP8 exclusively. Unless the apps have HW demands that require WP8, it will make no sense for a developer to target a minority only, when he can target that minority AND the majority by creating WP7.X apps. It is not a optimal situation, but the theoretical implications can be made to be much larger than the real life implications. Of course, the closer we get to the release of WP8, more people will hold purchasing. But this is no Osborne effect, this is only natural because people like having the newest bling.
WP7.X users will be the majority for a long time