Speaking of buying DRM-free books, let me mention again The Humble Bundle. Not many books in there, but for a good cause: https://www.humblebundle.com/
Schneier's last book, Data and Goliath IIRC, was also available as an audiobook, so I bought it, listened...until it ended abruptly at 1/3 of the full length.
“But please note that eBooks.com uses Adobe DRM to protect most ebook files, so the device, or the software running on the device must be compatible with Adobe DRM. If you'd prefer to obtain your books without DRM, you can browse our DRM-free section.”
Yes, unfortunately this is the case (I work for ebooks.com). Most publishers require us to use DRM and Adobe DRM really sucks, but there isn't other options out there and we don't have the resources to make something better.
We focus quite a bit of effort on educating publishers about moving to DRM-Free as it makes everyone's lives easier and from what we've seen increases publisher sales numbers.
Is this a regional thing to buy without DRM? I just checked some books from my reading list and many have DRM. Just some examples if you could double check:
Double Star
Project Hail Marry
Children of Time
A Memory Called Empire
This is How You Lose the Time War
While I know/assume that it will be easy to remove the DRM, I do not want to install Adobe Digital Editions to download the books.
I end up paying a big premium in practice over Kindle DRM and discounted paperbacks, but I'm doing my part to convince publishers to offer DRM-free.