Beyond the (alleged) goal of padding the length of the film, I think the extended wedding scenes came from writers struggling to give the audience any reason to sympathize with a group of unlikable characters. When your protagonists are drunk assholes who drive recklessly and aren't perturbed by women getting slapped around or having guns waved in their faces, and who possibly enlisted as an excuse to shoot Vietnamese people ("Kill a couple for me!"), it's hard to care when they're subjected to the horrors of war.
Paul's opinions this week strongly echo my own. I appreciate Platoon for its hyperrealistic portrayal of the war from someone who experienced it firsthand, and Apocalypse Now as an impressionistic fantasy based on "the war" as it diffused through American consciousness. I don't feel The Deer Hunter adds anything new to this duality, and I don't think it belongs on the AFI 100 for that reason.
Also, I see Paul and Amy getting some pushback on Twitter for discounting a queer interpretation of The Deer Hunter. When Cimino has demonstrated so little interest in subtlety for the majority of the film, I can't imagine him playing coy about Michael and Nick's sexuality, especially when the simplest explanation (Michael pining over Linda while feeling honor-bound to not pursue her) slaps you in the face every five minutes.