"Yeah, to a degree. It's most prominent in... traditional households. They believe that if the lineage keeps to a kind, the magic will be stronger. There are some pegasi on Cloudsdale who hold that kind of belief, thinking 'pure' pegasi fly faster. Since, you know, only pegasi can safely live there without issue, it'sa surprisingly large amount of them that hold that belief." Derpy explains. She seems a bit sour about the notion... which I understand.