I really hope they didn't ruin those cards for the sake of a publicity photo..
hopefully they're just dummy casings or something.
Nope, this is the story behind that photo:
1) nVidia didn't do that photo, it was some enthusiast who sent that photo to nVidia and they posted it on their facebook for him. The cards/casings are real.
2) The guy in question did a fully watercooled tri-SLI build with those cards, i.e. he ripped off and threw away the reference coolers anyway...so he was free to get reference coolers as dirty as he liked
3) As for the PCB's of the cards, look closely and you'll see paper napkins to stop the food (well, the wet food anyway) touching any of the actual electrical components