Thank you very much for the links. Unfortunately, they only confirm what I'd found so far. They all have the same eight or ten new books, several metric cart-loads of series books based on movies or video games, and a small mountain of vanity publications. Some have reasonably good selections of old SF books, but I grew up with a collection of a few thousand SF paperbacks dating from 1940 to 1970-something.
Regarding Baen books, I checked there but was rather disappointed. Many of their selections weren't actually available, and they seem dedicated to this "webscriptions" format, in which you get a few serials of their choosing every month.
I guess it really is a Mobipocket world. And while I appreciate the advice to improvise, adapt, and overcome, I come from a military family, and I've known enough Marines to know you stop improvising some time before the MPs come clobber you and cart you away.
Regardless of how one may feel about it, DRM has the law behind it.