You're right to remember that those number are JUST averages, meaning that half of the class has a GMAT score below that number. Our general advice is to try to at least be above the lower end of the middle-80% range for a given school. They usually publish that number. As long as you're within that range, you should be okay.
But, to answer your question about who gets in with a low GMAT: Those people are all outstanding in some way. Some have ad amazing careers, some have great personal stories of overcoming adversity, some have taken big risks and succeeded (or even failed), some are natural born leaders, and some are extremely involved in making their communities better. There's no consistent pattern other than the fact that there's something special/memorable about them.
They're the kind of people you're glad you know and just like being around, whether they have a 600 or a 770 GMAT!
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