They paper like crazy in NY; they'd rather give industry folks free tickets, than sell at a deep discount. "Everybody" seems to imagine they're building word of mouth for a tour or later life of the show.
But on Broadway at least, I hear that has something to do with the "average ticket price" which has become so important in all the reporting, even the real papers. My guess: - if it's low-price, it lowers the average, it it's free, I guess it doesn't count at all???