True. I guess they are technically within their rights to say a pound equals whatever they want it to. It's loose language on the certificate. They could say "Our current rate is 1 USD = 1 GBP = 1 Euro. Have a nice day."

Luckily, I've been able to agree with the front desk on exchange rate in each case where I've used a PP. The fact is that most places either have no idea what the rate is or only know what it would be if I was presenting an actual British banknote that they would need to take to their local bank for conversion into USD credit. So, we've used a copy of the Wall Street Journal, a Marriott.com printout, or a financial website to settle on the rate. That has worked so far.