The numbers don’t lie. This is 4,300 developers that were surveyed:
Now to be fair, it’s unclear if WP7 includes WP8 but presumably it does and the drop for WP7 is in line with the drop in Windows 8. Considering they are playing catch up with both operating systems, that’s not a good sign.
Of course, they will pick up when Windows 8 lands and Windows Phone 8 lands, but this seems like the old cycle where we’re always promised that the next release is the game changer.