Thank you for that, Hitch!
I cannot imagine an e-book without an actual (html) TOC. While it's true that novels didn't always (or even most of the time) have a table of contents, that has been changing over the past several years--in large part, I think, because of e-books. First, the TOC is a great sales tool in Look Inside on the Amazon store. Second, you can't dog-ear an e-book page, or fold in the dustcover end flap, or even put your finger there where you left off. And the synching option doesn't always or even most of the time actually synch to the Last Page Read (or you have messed it up by checking an endnote). So the Go To / TOC function is really incredibly valuable in a Kindle.
So I too have settled upon the one format fits all approach to e-book publishing: an epub, built by Sigil, that includes a cover, an actual/html TOC, and an NCX file. Following your advice, I have acquired a Nook, and my books look fine on the B&N platform, as they do on the iPad, iPhone, e-ink Kindle, and Fire. I don't publish on the Sony platform, so I don't worry about the Sony Reader. Kobo doesn't sell enough books for me to justify buying a Kobo reader (I would buy a Paperwhite first) so I am leaving that to fate.