The main uses for the USB socket are:
1) charging
2) side-loading.
Amazon patented wireless charging some time ago, so they won't need the USB socket for charging in the future.
http://www.geekwire.com/2013/future-...vice-displays/
And removing the USB socket would makes sense. It would make the Kindle simpler and more self-contained, it would reinforce Amazon's walled-garden (no more hardware side-loading), and as sweetpea said, it would make the device easier to water-proof.