> Bots often mimic the User-Agent of a common browser, but the version numbers used in the bots rarely change. Over time they drift farther and farther behind until a point (maybe two-year-old versions) where you can safely block them without inconveniencing legitimate users.

This supports the idea that browsers are subject to constant change and everyone should be forced to come along (rather than respecting and supporting standards). I have a Chromebook that stopped receiving updates some years ago (thank you for your very safe and sustainable product Google!), his heuristic would litteraly block me.