Partly because of my presbyopia and partly because of the problem of storage space in my library, I started buying electronic books in English about three years ago. Many books published in English after, let's say, 2000, to say nothing of new ones, are also available electronically, be they academic or not. Now most of the books I buy in English are electronic. Two open formats are used for these books: PDF and EPUB. They are better suited for academic and non-academic books respectively.
My favorite electronic bookstores in English are eBooks.com for books in PDF and Kobo Books for books in EPUB (this bookstore has a number of affiliates around the world, so depending on where you live, you may be redirected from the address I see in Israel - http://www.kobobooks.com/ - to another one). Both of them protect the books they sell with Adobe DRM, which in turn forces their readers to use Adobe Digital Editions, which, in my opinion, is a very heavy and intrusive electronic book reader program. But because of this protection you can't use other (and better) programs - my favorites are SumatraPDF for PDF and Bookviser for EPUB - unless you remove it. Fortunately, I could easily find ways, both free and commercial, to remove the protection and start reading my purchased electronic books with these favorite readers of mine.
The situation of electronic books and bookstores in Hebrew is still much more primitive than in English. A few academic publishers have started to distribute their books electronically, too, but I haven't tried them yet. For non-academic electronic books Mendele seems to be the biggest electronic bookstore, but again I haven't tried it yet. One thing I know is that it used EPUB and its books are protected by Adobe DRM.
The situation in Japanese is really deplorable. There are a growing number of electronic bookstores in Japan, but unfortunately, most of them use proprietary formats and force their customers to use their reader programs. This is why I hesitated to use any of them, just as I refuse to buy electronic books from Amazon and its affiliates as they also use a proprietary format. I don't know whether it's these bookstores and publishers who are too stupid to make a consensus to distribute electronic books in PDF and EPUB, which are two default (or often the only) open formats used for electronic books in many parts of the world, including the United Kingdom, the United States, and even Israel, or it's me who is too stupid to understand some ulterior motive of theirs behind this seemingly stupid decision.
I used to check the websites of major electronic bookstores in Japan and their review sites to see whether they decided to switch to PDF and/or EPUB. About two weeks ago I stumbled upon a few review sites, writing that Rakuten Kobo Electronic Bookstore uses EPUB and it's the only electronic bookstore to do so in Japan. My curiosity got the better of myself, so gave a try to purchase one electronic book there as an experiment.
I don't know if this bookstore really used EPUB, but the fact remains that you are stuck with its reader applications to read its books. But since I read only non-academic books in Japanese to get new information and broaden my knowledge on various topics, I've decided to keep using this service. In spite of this technical limitation, I have to confess that I enjoy this old-new intellectual pleasure and was reminded of the days when I still lived in Japan - I used to visit a few big bookstores on Friday, buy several new (printed) non-academic books, and read them on Saturday.
I also realize both from this pleasure and from my recent visit to Japan that Japanese can be a great source of new information, if not of deep knowledge, and after all, it's also my native language. So it's a pity not to use it. When I immigrated to Israel a little more than ten years ago, I thought I would have to give up my weekly pleasure of reading books on diverse current topics in Japanese, which was what happened, until I was reconnected to this world.