I find it odd you mentioning how closed iOS is and ye you carry a Kindle. The others readers offer ePub support which is obviously an open format.
Anyway, I use my Nexus 7 for: reading books (take your pick: Kindle app, nook app, Google Books, Aldiko or Kobo); Google maps is excellent (most of the Google apps have been optimized for it); Google Reader or FlipBoard work well; it’s quad-core CPU and 12-core GPU so much better than the Galaxy Tab (but also because it’s stock Android, none of that TouchWiz nonsense).
I see the confusion, but the truth is that I can** put by one means or another _any_ open content onto the Kindle because “it’s just words” – so Kindle’s adherence to the FOSS-blessed format du jour is not relevant to me so long as the Kindle does not inhibit me from adding stuff to it.
Frankly I am most annoyed that it lacks a decent .TXT and offline HTML viewer; but HTML I tend to post on the web and view from anywhere, anyway…
And it’s unusable as a content-creation device, so I don’t worry about it not writing in an open format because it does not write at all.
I should get to play with Simon Phipps’ N7 today. We shall see.
And he can put me right about the format issue, too, if needs be.
* isn’t that ironic, in retrospect? 🙂
** by means of geek uberness if not brute force