Really, it seems that once you're approaching 50 a life-time of smoking takes it's toll. Plus, I think that lots of smokers just give up on their teeth because they going to get stained anyway and they don't see the point of maintaining them if they're always going to look like crap anyway. When you're younger, the enamel is good so teeth are less porous and clean more easily even if you do smoke. My pal Pete's teeth have just rotted away with all of the cheap cigars that he smokes. His breath smells of old cheese and is quite repellant.
But he's still my pal even if he does smell.
Englishman.