A vital fact that most American watchers of Buffy will have missed is that "Giles" had a previous existence as one of the most well known characters on British TV as the Gold Blend man, a principal character in an interminable series of "romantic" instant coffee ads somewhere back in the big shoulder pads era. Which did get granted a token in-joke ("God, this coffee's disgusting") somewhere near the beginning of the Buffy-goes-to-college series, which is currently running on the BBC, no doubt a year or two behind the USA.
(update a year or so on): Anthony Stewart Head currently has a role in the BBC's comedy series "Manchild" playing a 50-year-old divorcee with an eye for much younger women (but suffering from a few technical problems). He still comes over as if he's playing Giles, though maybe it's just the accent.