I work with a number of sales folks who changed my impression of what it means to be a "drinker." I know personally several people who will easily and regularly down a few (3-4) 4-ounce vodka martinis before dinner, split a bottle of wine at dinner, then drink five spirit-based drinks after dinner.
More than one of these folks has admitted they simply "don't get hangovers." They could be lying, but with the amount of alcohol they can drink and still be perfectly functional the next day, I bet these folks skew the average.
If you're drinking regularly and in large amounts like that, your tolerance for alcohol is going to be quite high, and your hangovers much more benign. If they quit drinking for a few months and then tried to drink like that again, they probably wouldn't make it through the night, and the next day would be rough.
More than one of these folks has admitted they simply "don't get hangovers." They could be lying, but with the amount of alcohol they can drink and still be perfectly functional the next day, I bet these folks skew the average.