IDP's are only valid for a short period of time. I suspect that money-grubbing may play a role, but the purpose of them is to let you identify yourself to police in a language (especially an alphabet) you don't speak. So perhaps it's something that clerk had heard some horror story about and was giving good advice.
Yes, I suspect the 1 year validity of the IDP plays a part here. The gentleman who said my photo wouldn't be accepted was front desk (and, apparently, photo-taking) staff; he wasn't even the person creating the IDP. I agree with you that I suspect he was trying to be helpful.
$9 isn't worth being detained while on an international trip in a place where the police don't speak your language because they don't believe your photo is you. Actually, it's less expensive than the last set of passport photos I had made, so maybe I'll just go to AAA next time.
