Password protection, besides for being offered, is also meaningless if you are worried about political persecution over your reading habits, you need file/disk encryption.
I cannot see Amazon/B&N/Kobo/Sony/anyone caring about going that far. Tablets are an obvious better choice due to the wealth of options available. Ereaders are not The Land of Choices...
And I do hope you perform full-disk encryption on your computer as well.
Keep in mind that there are many ways for obtaining the preserved decryption keys if you aren't careful, no matter what the device. They may simply hold you down and take off with your device, then extract the keys from the RAM.
Really, this stuff is just way too much work to be worth the time on devices marketed for casual users not specific to politically charged environments. It will not happen, and I will completely fail to be surprised at that.
https://hurricanelabs.com/blog/attac...cryption-blog/
http://www.cnet.com/news/disk-encryp...esearch-finds/
http://www.techsupportalert.com/cont...not-enough.htm