Indeed the sight of those 747s at Gatwick in 1972 was a pretty spectacular sight. Particularly as two of them, including the QANTAS as far as I can recall, were parked on the 'diagonal' stands at the end of the old southern pier. The roof of that pier was the viewing terrace at the time of course, and from the western end of the terrace, which wasn't surrounded by a high security fence or glass, it almost felt as if you could reach out and touch the 747s!
I agree that the claim re the first QANTAS flight undoubtedly meant it was the first planned service to the airport by the carrier, but the wording that Dave Reid reported above was exactly the same as the words I heard from someone at the airport (i.e. specifically "the first QANTAS aircraft to land at Gatwick") so I suspect there had been an internal/staff briefing on the subject that used those very specific words. Perhaps I'm just a stickler for precise and accurate wording, but I couldn't help myself and had to point out that a QANTAS aircraft definitely had landed at Gatwick before ;-)