I only ever remember the repeats shown since 405 lines (on 625 and digital), and I don't think it is down to quality at all, as there was nothing wrong with either sound or picture. In fact many digital channels seem dedicated to the older stuff anyway - maybe not that old, but not ultra worthy of the technology today, if you get my drift.
They are funny, but given the amount of stuff around, even if the beeb had the rights to show (dunno if they have or haven't), they would probably get flak for it because it is so old.