Was almost unable to rent due to booking internationally

I was told that I would be unable to rent the car because I had made an international booking and didn't have a international drivers license. I have a US drivers license, even though I reside in England. This was extremely frustrating and almost resulted in me not being able to hire the car. Upon booking, I saw a list of acceptable IDs, which included a US drivers license. The manager sorted it out, luckily, and I was able to hire the car after all. But I had an extremely negative experience with the person at the counter and whatever policy she was referring to seemed totally absurd. Why would I need an international driver's license if I had a US one?!