Not to go all Liberal Arts here, but vacation comes from the Latin 'vacare' which means 'to be free' or 'to be at leisure.' Holiday, though, is from holy day, which still makes sense to some degree (Christmas, Easter, Hannukah breaks, vacations, etc.), but in a society where "vacations" aren't strictly tied to feast days or holy days, then vacation probably makes more sense.
The chances of them each having 20 kids is highly unlikely, of course. But let's say they did. That would be 400 people over the course of 30 or so years. In the time it took me to type this, about 200 people died. That combined with the fact that birth rates are WAY down across the globe (and steadily shrinking), and I don't think you have to worry about the Duggars taking all your water.
Because they threw snowballs at Santa Claus 30 years ago, which as we all know is worse than routinely beating the shit out of and/or murdering people. C'mon, Petchesky don't you read your sports media memos?
@nicnack74: I may be wrong, but I think it was just meant to gauge how accurate the numbers were...if not counted, that's a significant percentage of people that we're "missing" in regards to the census.