I hadn't heard that - is it on the AAA website? We went on the tour a few weeks ago and I paid $44 each using my Disney Visa. I think that was a 20% discount(?) We thought it was well worth it as we went on a very crowded Saturday and did they last tour to get reserved seating for the fireworks. $39 would be a bargain.
The AAA discount is a regular thing. Also, if you book your vacation using your Disney Visa, you also get the discount. We did this in July and had a great experience.