I have a Kindle and a Nexus 7. Both are nice devices, but serve very different purposes. You can certainly read on the Nexus 7, but it's an LCD screen: eye strain. Also, there are continuous distractions, and sites like this one are just a few taps away.

Taken all together, this means the Kindle is way better for just reading - you can really lose yourself in the book, something that I can't do at all with a regular tablet.