I would have thought that too, but my mom tried to buy a used car with a check recently - for my sister who had moved, and needed the car immediately - and it took them almost three weeks to "clear" the check and give her the car (the check had cleared at Mom's bank within three work days.)

A lot of dealerships don't seem to be able to handle someone who just wants to buy it outright without credit and drive off. (I suspect any dealership that *was* set up to expect people buying outright without credit would be very happy to take cash.)