I have acquired a Kindle. It is an older model and has no bells and no whistles (thankfully). It is strictly a reading device. It also happens to be the best way to read simple literature in a digital form.
However, if I want to read any of the “reams” of documentation I currently keep in Dropbox for the various systems we are using or plan on using at work … I reach for my iPad Air. If I want to read a programming book or some sort of manual then I also reach for the iPad Air … or maybe even a machine running Mavericks so that I can have Xcode or TextMate nearby.
This is only one example of how different tools (in this case: devices) are better at some jobs than others. I could read my fiction on the iPad or even the iPhone, but the Kindle is just better for doing that sort of reading for any number of reasons. By the same token, I could email the documentation to my Kindle and read it there, but the iPad is just better for reading documentation (especially large PDFs) and also for working through programming books.
Take it a step farther and there are some things that the Kindle and iPad are just not capable of, and that is alright. I feel like the Kindle would be worse in some non-trivial ways if it was trying to be more and the iPad would be worse if it were trying to be more. The idea of converging every task into a single device is a nice idea, in theory, and can end up being a terrible thing when brought into reality.
Reality has a way of doing that, by the way.