Also Bought

While getting ready to release Firebase I was told I should pick out some books of a similar nature to help identify my genre and likely readership. I picked three, The Sand Pebbles by Richard McKenna, Message from Nam by Danielle Steel and A Saigon Party by Diana Dell. Now that Firebase has been on the market since June, it has an "Also Bought" list on Amazon on which none of those books appear.
The reason I mention this is to recognize how useful the "Also Bought" list is, not just to readers looking for more books, but also for authors to find out what other books their readers like. If anyone has had a similar experience, please let me know.