I think it's an acknowledgment that the lines will not always be in the same place.
If I for my home campaign want to have cultures derived from ones that aren't my own, that's one thing--I can take some reasonable care to make them not stereotypes, and the people around my table/s know me and trust my good intentions. It would be a vastly different thing if I were trying to publish my setting, without doing more work, without hiring cultural sensitivity readers, and such--there's simply too much history for people who don't know me to trust my good intentions.
(And--not unreasonably--if J. Random Whiteguy writes a setting without non-Euro cultures, Mr. Whiteguy is probably going to get raked for whitewashing his world.)