There is a problem in Dreamweaver that it still expects the DOCTYPE whereas it is actually not required for xhtml5. This is more of a Dreamweaver issue rather than an export issue with InDesign.
So, is that solved in Dreamweaver CC or is it still an issue to be fixed?
It is not fixed in Dreamweaver CC. One way is to add DOCTYPE to the xhtml file: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> manually and then try opening in Dreamweaver. It will then show the ID generated CSS.
Actually, you just need <!DOCTYPE html> and not all the rest - epubcheck will complain about the external DTDs.
In the next update to InDesign CC we've put this back in the files for EPUB 3 so this particular annoyance will go away.
Architect, InDesign Engineering
Fixed in 9.2.