I have the same reaction. I always tell the desk clerk that AARP should not rate a discount. Fortunately, there are several other ways to get discount. I am a Federal Employee and frequently can get a discount, even when I am not on TDY. AAA discounts are usually the same.
On a recent 4000 mile trip I actually had a motel clerk ask if I had a military ID. That was good for the discount. I sometimes ask for commercial rate if I'm on business. I agree, AAA is a much better organization to belong to when in search of discounts.
"I always tell the desk clerk that AARP should not rate a discount."
I'll bet that's just the highlight of the clerk's day. What's he expected to do about it, exactly? :)