I think 99er, while maybe a stereotype, is not a stereotype based upon one's race, ethnicity, or national origin. Rather, its based on an individual's experience, and an a experience that is relevant to the subject matter. Certainly people that never paid any attention to the Tour prior to 1999 have a different frame of reference than people who have followed bike racing for a number of years. (and I think my use of the term was to say I wasn't a 99'er, rather than to put down a specific forum member because they were.)
Back to Seppo. I personally am not too concerned about political correctness. However, inconsistency bugs me. Everyone would certainly agree that use of the N word is inappropriate. There would also be broad consensus that calling a person of asian origin a number of slang terms that I won't repeat would be offensive. Frog, IMHO, is no different in charachter, nor is Seppo. I guess what bugs me is the idea that's its somehow ok to be derogatory of Americans. What if we started calling all Australians convicts? Would that be acceptable? It certainly wouldn't be constructive.