Not true in that broad sense. With an AP you can get certain dining discounts but not everywhere at WDW (most are actually at Downtown Disney)and the small number of in park ones (like at Epcot) are for lunch only. The dining discounts vary from 10% to 20% when avaialble. With an AP, you can purchase a Disney Dining Experience card ($65) which is good for a year and that card does give you 20% discounts at almost all WDW restaurants (but there are a few exceptions, e.g., Japan's Teppanyaki does not take it).
The AP 10% merchandise discount is good only at certain Downtown Disney stores (like the big Disney megastore there) and not at any of the park or hotel stores)