No, InDesign actually always exports a class. But it's a feature request I strongly support to have the choice of adding classes or not. I've reported already the FR some time ago. You may do the same?!
I did report as a feature request, although it seems more like a bug to me since the feature was available in previous versions. Thanks for the tip.
You are right that this feature was available in previous versions but since "Emit CSS" functionality was added, the behavior changed and we started exporting classes always in out EPUB output. We have heard from a lot of users about this feedback and we will keep this request at priority while addressing EPUB specific issues.