A linked TOC and CSS are integral parts of ebooks.
I don't see the need for a TOC when the author didn't see the need for a TOC. In any case most PG books don't correctly link TOC on Kindles.
The problem is that the CSS has to be designed for use with ereaders.
And historically at least Kindle and kindlegen have very weak support for CSS and interpret it considerably different than modern desktop web browsers. Thus, for example, grabbing the last 10 books PG has published, I find that 6 out of 10 books have serious broken formatting on Kindle -- and arguably 10 out of 10 -- are ill-formatted on pretty basic grounds -- i.e. "What is the correct way to format a paragraph?" Don't know if the kf8 tools if and when they are actually release will help this any.