I think the GMAT also matters more depending on what pile you are placed in. Obviously you have the Indian IT, where the overall average is probably on the higher range of the GMAT. Then the IB from NYC who apply in large numbers probably overall a tough group with a below avg to avg GMAT.
I used to think that schools demand higher scores from the Indian IT pool. I think this is a classic example of mistaking a correlation to a cause-effect. (Those CR days!).
Indian IT applicants with the high GMAT scores probably are better prepared and more hard working than the other applicants with lower scores. I said probably, so please dont take offense.
A high GMAT indicates that he/she is willing to work very hard to improve the odds of admission. Now, wouldn't such a person naturally put together a better application than a person with a lower score. I am sure people with 780 do crappy applications and conversely someone with a 600 can do a great job. But on average, you will expect the high GMATers to do a better job than a low GMATer.
Consequently, the high GMATers from the Indian IT pool get in more than the low GMATers. But they get in not neccesarily due to the high GMAT. But I can see how this can create an impression that a high GMAT is neccessary or sufficient.
Re-take GMAT if you feel you underperformed, but dont do it just because you have the need to crack the 750 barrier. My 2 cents...