This discount is on the version that you have to hook to your computer in order to update. A single $25 discount seems inappropriate for this devices.
I would rather see a discount on the free-3G/wifi version of the unit. In this product, you get free 3G for life. An ad-supported model makes more sense because you continue to receive a service in exchange for continuing to receive ads. It would also allow them to update those ads more often.
The best solution would be to discount the reader a bit *and* discount each kindle book you buy, say maybe by 10%.