you clearly sound like a guy who has never had to try to get another guy off after he popped once already. Here's a clue Steve...IT TAKES ALOT MORE WORK.
OK let's simplify this...
GUY A pays for one hour. He likes to take his time. Maybe start with a light sensual massage, Plenty of foreplay, different positions and then when he's ready POP.
GUY B pays for one hour. He walks in, strips, shoves his junk down the girl's mouth pumps her face for 2 mins and blows his load. The girl now has to spend the next 30 minutes trying to get him back up again. This can take plenty of energy and work from the mouth, hands, pussy, etc. and now the guy is hard again and takes another 20 mins of hard pounding to pop again.
Given the work level the provider has to do in the two above situations, don't you think you would charge extra for GUY B?