I'm just guessing, but the serations could hang up on harder materials like bone, because just below the point of the seration, the angle relative to the shaft is quite steep. But I also think that some of the concern may go back to a time when one had heads with large cuts in them, and sometimes they would be quite difficult to sharpen. These days, with so many using some form of replaceable blade head, where the serations are razor ribon steel, sharpness isn't the issue.

While I would guess that serations work great, I can't really see why they would be any better than a razor edge.