Yeah, the tablets are based on a whole different design. The books are IIRC in an Android appdata folder somewhere hidden, (although you can probably find it with effort, calibre can't) as opposed to the mounted userstore on an e-ink which is by design easy to find.
The tablets are Android, the e-inks aren't.
And Alf didn't invest in finding out how to fix the DRM on the Fires either, but that's a story for elsewhere (read the blog).