I purchase a large number of books every year. Back before the days of the Kindle and iBooks are used by paper books. These were typically nonfiction text all manuals. Over the years since I have been purchasing management guidance. In the last few months I have picked up a number of Malcolm Gladwell books as they seem to be garnering favor in the executive branch. I have also been downloading a number of technical papers as PDF files from a number of University research projects. While anything purchased on my account at Amazon is automatically downloaded to all of my Kindle devices and software instances the same is also very true of iBooks and purchasing media. The same cannot be said when loading PDF files.
Trying to read a PDF file on the traditional Kindle is near impossible. Fonts are simply too small so it is not a practical device to read PDF files. Since I have not tested a Kindle fire I can't say if same applies there. But when it comes to other types of media like video and audio iPads and android tablets seem to have paved the way.
Going back to my PDF files and downloading them onto my iPad they simply do not sync between all of my devices. PDF files will only sink if I import them into iTunes directly and then synchronize my eye device directly with iTunes.
I cannot tell if the designers over at Apple failed to imagine all of the use cases that were necessary for a successful iBooks reader or if they simply do not have enough time to complete the task.