I only have the USA DVDs of Buffy the Vampire Slayer. AND I had no clue about this either. Is it the same on the ANGEL DVDs? I haven’t checked in awhile.
I’ve the full series of both on DVD.
I don’t know about Angel but I wouldn’t be surprised if that was the case
you can sometimes actually hear the music from the “previously” segments abruptly cut into the opening of the episodes on the US DVDs as a result of the removal of those portions (it’s ESPECIALLY jarring for the episode The Gift)
Fox in general seems to have a fetish for doing that because the same thing happened with The X-Files