Generally, when someone describes the highs as "rolled off", they feel like the high's are dropping off before 20,000 cycles. Generally, a flat frequency response is desired between 20Hz-20kHz (typical child hearing range). I would guess that many/most of the users here can't really hear much above 15-16 kHz.
Philjolet is correct in calling it arbitrary. Some prefer a perfectly flat frequency response, others prefer rolled of highs to keep your average recording from getting too bright.
Philjolet is correct in calling it arbitrary. Some prefer a perfectly flat frequency response, others prefer rolled of highs to keep your average recording from getting too bright.