I think the popularity of stock car racing has seen most of our talent invested in that area of racing. A lot of talent from Indy/Cart has moved over to the NASCAR ranks. On the other side, very few drivers have made the jump from NASCAR to open wheeled racing. Even the few that did are/were mainly stock car drivers at this point. I dont think either one is harder than the other on a whole though, just a different skill set.
Strip
Yup, i think Scott Speed is some stock car league now. Juan Pablo Montoya even left F1 for NASCAR.
I just can't get into NASCAR, I like corners, and braking, and right hand turns. I mean, I know there is tremendous skill in NASCAR, but it's like golf, in that even though it takes mega skill to do well, it's about as exciting to watch as drying paint. I'd rather blow torch my nipples off then watch 4 hours of loud, sedan look-a-like cars go in circles.
Edit: I recently have seen some old videos of the British Touring Car Championships, back in the day when it was 4 cylinder Cooper Minis VS. V8 Mustangs. Those were some neat races, with the big muscle cars pulling away on the straights, and then the little Minis out braking in the corners and slipping past. Now the BTCC seems to be all little hatchbacks, not nearly as exciting IMO.