Amazon has pulled out all the stops in a recent firmware update for the Kindle Voyage, Kindle Basic Touch and the Paperwhite 2. This means that enterprising citizens with a proclivity towards exploring the inner workings of the software and modding it are thwarted.
The new firmware was pushed out to all modern Kindle devices in late November of last year. Anything after version 5.60 will not allow you to hack the firmware and do interesting things like change the screensaver system or install custom apps.
Amazon really is hellbent on locking down their entire ecosystem to prevent easy access to mess around with the Kindle software. They are chiefly doing this because they want to dissuade the reverse engineering of their operating system and to prevent hacking.
Locking down ecosystems seems to be the trend right now in the e-reader industry. Barnes and Noble has been getting a lot of flack from their customers when they eliminated the ability to download Nook Books. They said it was to curb piracy, but more likely they want people to use their official e-reading apps for Android and iOS and not the competition.