Hitch,
My Kindle Fire HD definitely uses the NCX file for its "Go to" menu on KF8 books; whether purchased or built by me. I know because: 1) all nested ToCs collapse and expand like they should. 2) my NCX ToCS are rarely identical to my html tocs. 3) I can go to the html toc
from the ncx toc—you know... that thing that drives wolfie mad?!
I was told that the Paperwhite and the Touch all were capable of using the NCX file (if it's present) for KF8 books as well. I just wasn't sure if the Kindle Keyboard did.
Are you certain you're just not seeing an ncx toc that's identical to your html toc?