I agree, it's arrogant. I ride in large groups like that all the time and sometimes we let cars build up behind us but as soon as there is a clear shot we ride single file if possible and wave them on. In my state two abreast is legal till there is a faster vehicle wanting to pass. 4 abreast is not sharing the road and indeed would piss off your average driver.
Sometimes though it's safer to travel in a tight pack then it's analogous to following a slow car (hazard lights on) or farm vehicle. Drivers won't complain about the farm vehicle as much as they would the bikes though - go figure. IT would be very dangerous for cars to pass 20 riders single file around a corner and when drivers approach and see riders single file it invites them to zip right on by.
So it depends on the situation but four abreast none the less is not right.