p.s. sorry, I forgot (or You didn't want to mention it) another reason why EE, want to make device unrootable...
it's to force people buy books from EE's shop (To make a little harder proccess of viewing or purchasing books from other stories, or to protect books from DRM removing)...
But again it's useless...
1. all DRM protected keys on EE is unencrypted (hashed but it's not a problem for anyone). So another security hole in EE.
2. again there's no problem to download books without EE, or copy them from EE without root.
3. DRM by itself is suck, and removing protection (no matter if DRM or PASS based) takes almost no time.
4. There's no problem to download any book that you're selling (or will sell) on torrents or book sharing sites.