back in the day there was a healthy blend of win95, 98, ME, XP, and vista in the wild. it was common for devs to check for older versions with something like `if str(os.version)[0] == 9`. according to legend enough (internal?) software kept breaking that the solution became "don't put a 9 in the version number".

iirc they officially stated it was because of how much people disliked win8.