Do keep in mind that mining sales EVEN FOR AMD are a very small part of their overall sales - even on the higher-end cards Miners prefer.

 For NVidia, it's not a noticeable factor at all as they've rarely been overall competative on any GPU-based coins.
 THEIR stronghold is Folding@Home and the like - and that's a very small factor for them (except perhaps for EVGA with their long-standing FAH support/reward program).