Brian,
I think averaging 80 is about right. Like you said, they're not playing it all the way back -- in addition to some of the up tees, 2 and 18 both usually play as par 5's -- but the setup has got to compensate for that and then some. (Is the 77.0 what a scratch is expected to average, or is it what a scratch should average in his best 10 out of 20 rounds?)