My ebook reader (a Kindle) uses an HTML-based format. No ebook reader I know of uses PDF.
My favorite websites to read are not PDF. "Fidelity" is not important to me...being easy to read on the device I'm reading it on is what is important to me. In fact, I find it painful to read a PDF on my computer, whereas I read tons of documentation on web pages without trouble.
Finally, a web page today can look like pretty much anything, including a "book" layout. PDF isn't necessary or useful. Fonts can be embedded, styling can be done down to the pixel level, scalable illustrations can be embedded in SVG, etc. The only reason people don't lay out stuff on the web like a PDF is because it's not as functional as treating it like a web page.
I have genuinely never experienced this, even on a Kindle. The books I read have pleasant layouts, which I feel is only because the designer works on a fixed page.
That said, I have been reading material from http://www.accountingcoach.com and the author has got good design on pretty much all browsers I've used, including my iPhone so I suppose it can be done.
PDF is the preferred format for reading textbooks and journal articles on e-readers. With a large-size e-reader it works well. The only real competitor to PDF is DjVu.
It is not the default format, and if you'd ever tried to read a PDF formatted for big screens on a Kindle, you'd know that it's a horrible experience. The default format for Kindle is mobi, and many others used epub. My point was that though I read books exclusively in digital form, I never read them in PDF format. I don't miss the "fidelity" of PDF; I want the book to be comfortably readable on the device I'm reading it on, and PDF is never the best choice for that.
The Kindle does have PDF support and has for many years. However, people rarely use PDF support on small-screen devices, and nearly all Kindles are small-screen.
My favorite websites to read are not PDF. "Fidelity" is not important to me...being easy to read on the device I'm reading it on is what is important to me. In fact, I find it painful to read a PDF on my computer, whereas I read tons of documentation on web pages without trouble.
Finally, a web page today can look like pretty much anything, including a "book" layout. PDF isn't necessary or useful. Fonts can be embedded, styling can be done down to the pixel level, scalable illustrations can be embedded in SVG, etc. The only reason people don't lay out stuff on the web like a PDF is because it's not as functional as treating it like a web page.