When I first heard about this survey, I sort of fixated on the word "moment," and one that quickly came to mind was Jim McKay saying, "They're all gone" when he reported that the Israeli Olympians had been killed in 1972. There was something so gripping about those few seconds and the way he delivered that line. Pitch perfect. And I would also give a strong vote to the Apollo 11 moon landing.
USA-USSR hockey was on tape delay for everyone not near the Canadian border (CTV broadcast it live). Kind of disqualifies it from being a TV "moment" (although I guess those who watched who didn't know the outcome would disagree). On the moon landing theme . . . I would say the first images of Earth from space and the Genesis reading from Apollo 8 were memorable TV moments. And while more than just a "moment", the early days of the Iran hostage crisis were such good TV that they spawned the long-running "Nightline" show.