I'm a xc skier and my VO2max tested at 71 at my college's lab.
There is no way that is correct. If I'm actually a 71, then I'm the most under performing runner and XC skier of all time.
I'm guessing calibrations are not done correctly for most of these people claiming they are in the 70's to 80's.
If you test in the 70's and 80's, and I were your coach, I would recommend a big decrease in VO2 max intervals and a big increase in intervals focused on improving your efficiency at faster paces.
If you've got a big VO2max, there isn't much need to work on it more. Improving your endurance through longer, but less intense intervals is probably the way to go.
I have no evidence to back this up, but I improve most when increase the duration of my interval workouts (35-45 mins on time) and decrease the intensity. The races I race are long and rarely require high, short power outputs.