I bought probably about 20 books on O'Reilly website. Mainly because they are typically of good quality but also because they're drm free.

I always appreciated that they were available in any format (pdf/ebook etc) and thus easier to search. You can even sync them to your dropbox automatically after purchase. A download them.

We had a book service at a former company and it was terrible, one page at a time with a clunky web interface. Being able to download and scan them was much appreciated.

But as internet search gets better, you find quick solutions on stack overflow. It must be hard selling books.