I am afraid, you are going by what companies like Adobe has to say about standard eBook format, not what consumers of those eBooks has to say about it.

I would request you to do a research on the Internet and find some e-books on any topic of any subject, and then let me know what all formats (pdf, lit, .prc, .mobi etc.) did you find there. I am 100 percent certain, Pdf will emerge as a leader. Please take this opportunity to find some good e-books on the Internet.

Thanks
Bikram

“pdf has become de facto standard for eBook publishing for the web or PC, .mobi, .epw, etc. are closing in, but .pdf is still the preferred publishing format.”

I have no idea as to who you are, or where you are getting your information from, but even Adobe is not suggesting that PDF is the preferred eBook format.

Adobe has endorsed EPUB as the preferred eBook format.

http://blogs.adobe.com/billmccoy/2009/05/epub_generation.html

http://code.google.com/p/epub-tools/

http://www.idpf.org/