Yeah... and the same with DVDs: Buy a particular film, and see different editions (or formats) of the same film appear in your recommendations.
Of course, part of the problem with DVDs is that different editions/formats are catalogued separately. Wouldn't it be nice if, when you searched for a particular film, the search results page didn't list each version of the film separately, then the close or related matches in the same way - but instead, the first result was just the film you searched for, then each subsequent result was just one result for each individual film Amazon considers a close/related match.
Click on the page for the film, and there it can list different editions in the catalogue.
Note that if you visit the page for a version of a DVD you've already bought, it tells you at the top you bought this item on such and such a date. By listing DVDs in the way above, it could say you bought "such and such a version of this film on such and such a date".
Under the current system, if you've bought "Popcorn Blockbuster 3: The Sequel's Sequel - Ultimate Edition" and you forget, you could find yourself on the page for "Popcorn Blockbuster 3: The Sequel's Sequel - Final Ultimate (We Really Mean It Until The Next One) Edition" and buy it again.
If the underlying database is per film, and the editions are listed under that, the problem goes away. Indeed, if Amazon did it like that, I'd quite happily tell them what films I've already bought from elsewhere. Sure, they'd be more than happy for me to buy the same sodding film twice, but they'd be providing a better customer experience, and in return for that I'll happily give them more data to make better recommendations to me, and therefore encourage me to spend more.
And while they're at it, including an IMDB link for each film as well would be useful.