Stock cars at road courses is suprisingly common actually. Some times a touring car sanctioning body will invite some of the smaller stock car groups out to race with them.
If you said that they were made for both, but are usually used for ovals, then it would make sense what you are saying. But how it was it looks like your saying they are made for the oval, which if you add "only" it means the same thing.
I hate oval driving, but I would really love to see an 800hp V8 stock car in the game. I would prefer to drive that over any of the current GTR cars. Also, because stock car bodies are pretty generic, it should be easy to please race fans who want to make skins of their favorite drivers.