The biggest difference between this and the Hilton website is that, with Hilton, you can see the AAA rate and find the total cost with taxes before you have to put in the code. With Marriott, you have to put in the AAA number just to see what your total per nightly cost will be.
When comparison shopping and trying to do miles/money calculations, I like to use total cost with tax. It just adds another annoying step just to find out the full cost.
Maybe they could move it to when you are ready to book.
Lately, Hilton has been saving my AAA number as I have not had to type it in when using lately.