In which I commit heresy

Just before the 2 minute mark on the Fleetwood Mac song and just before 1:50 on the Pink Floyd one, there is a strong similarity (these are not the best videos--but the best ones I could find that were embeddable) in the musical progression. Both cases have low, wispery, chant-like lyrics and then the main motif of the song bursts-forth. I'm sure it has been done a million times, but Fleetwood Mac's version was done in 1979 and Pink Floyd did theirs in 1982. I won't deny the obvious differences--Pink's has their usual sinister undertones compared with Mac's sunnier sound. But still, I found it interesting. Until today I couldn't have said for sure which one came first, though I suspected that Tusk came out before The Wall.