Those where B&N "NOOK read to Me (tm)" books and are primarily kids books.
I've rooted and ROMed my Nook to have CM9 (Android 4.0) installed on my nook. With Moon+ I listen to TTS ePUB books all the time. For PDFs I use ezPDF.
I don't know if the default nook has TTS but if you rooted your nook device and isntalled Moon+ you might be able to use TTS on ePUB.