Depends if WP8 will be high-end only or more general.
If Nokia/MS continue WP 7.x on the low-end, there probably will be more WP7 phones sold in 2013 than WP8 devices.
But it is very sad to know that all the current Nokia flagship products (N9, Pureview 808, Lumia 900) run a software platform that will ultimately be abandoned sooner than competing phones with iOS and Android.