If I remember correctly, Theodore Gordon used a single wing of wood duck that was canted back.
A.K. Best ties in his wings with the the butts facing the eye, arguing, that over time, the wings will cant back. And of course, the Harrop Elk Hair Dun has the wing canted back.
My guess would be that it's just easier for a guy who may have to tie 10 dozen flies a day to tie in wings tip forward.