I guess I'm used to the flat-tops that have some kind of weird plastic coating. Over time (and not that long) they get crap stuck to them that just won't come off, and various scratches and gouges make them impossible to ever get totally clean. [EDIT] Which is to say, yeah, maybe all-glass ones don't have that problem (brittleness issues aside)

And I consider removability a benefit. It's much easier to scrub something at the sink than on the stove itself.