Sure it is. They get these stats wrong all the time; it's why they have to pay $600 for a couple volunteers to take a later flight because they've overbooked and got the estimation wrong.
Stats don't lend themselves to perfect predictions.
I doubt that's a case of getting it wrong so much as calculating the acceptable rate of compensation paid in order to maximize profits.
Most of the time, there's somebody who's happy to have the free travel. I've done it and the compensation was approximately one free transatlantic round trip in exchange for spending the night in an airport hotel. The cost to the airline is, of course not the face value of the voucher.
