Hi unlimited, welcome to MobileRead.
EPUB is just a file format, one often used by libraries.
You may want to post your request for ereader purchasing advice over in the
Which one should I buy forum -- you'll get lots of helpful suggestions there.
Briefly, since long-run reading is much more important to your husband than apps and games and web browsing, he'll be best served by one of the
E Ink Pearl ereaders. That used to just mean Kindle and Sony but recently the new Kobo Touch and NOOK Touch models also sport the paper-like Pearl displays. Kindles do not support
ebook library borrowing right now, but Amazon has announced support by year's end. (This should be in the form of a firmware upgrade available to existing Kindle 3 owners, so there's no need to wait for it.) Sony Readers, Nooks, and Kobos already support borrowing from libraries.