If the average user spent a few minutes online they would find that it is not difficult to buy from stores other then Amazon.
All the independent bookstores sell DRM free Mobi and EPub, so you don't have to do anything. If you want to shop at an ePub store you need to have a chat with Apprentice Alf and in about 30 minutes you are good to go.
Better yet, you take one look at the Amazon bookstore and realize that it sells pretty much everything Kobo, BN, Sony, Apple and the others sell and then some so you don't worry about shopping at different stores.
Sorry, but the "locked in" thing is bogus and has been for a long time.
Assimilation does not have to be painful. Here, have a cup of tea.