There will probably never be a WYSIWYGOEROT (what you see is what you get on every reader out there) editor. WYSIWYG simply means that you don't have delve into code (html/css) if you don't want to.
Learning the idiosyncrasies of the various devices on the market is an ongoing and mostly personal, hands-on endeavor. People share of course, but there is no central repository for the knowledge.
In this particular case, I suspect, the "pages left in chapter" feature offered by Kobo is more or less restricted to their slightly proprietary kepub format. Which—as it it seems I've been typing quite a lot lately—is NOT epub... no matter how similar the file extensions appear to be. I suspect that the Kobo-bought ebooks that it's working for for your friend have in fact, been downloaded as keypub files and not epub.
I can assure you that "pages left in chapter" is not any sort of standard ePub functionality (ePub meaning ePub2... which is what Sigil creates).
Last edited by DiapDealer; 01-10-2013 at 04:21 PM.