There have also been cases where a customer violated Amazon's terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
Takes a small effort to set up (install Calibre, install NoDRM plugin, apply Kindle serial to plugin), but once it's done, the rest is literally drag and drop, it removes DRM from your books automagically.
For Kindle specific ripping, I think it changed a year back and now you need to have a kindle connected before the Amazon servers poop out some magic unlock key/the whole book. After that you're golden, but during the rip you need a kindle device..
The last instructions I had involved downloading an older version of the Kindle desktop app to grab the books, and I couldn't find that one except on style rather sketchy looking sites that I didn't trust running executables from.
This looks like it might be a more effective solution. Thanks!