I wouldn't doubt that story. Usually, revisions are made specifically for those reasons. This pattern is nothing unusual (NES, SNES, Genesis, Saturn, etc, etc,)
But the end result is that Duo-Rs have been more reliable than the original Duo units, so unless you really prefer the aesthetics of the original Duo (I'm actually one of these cases), or you really, really want the headphone jack, Duo-R might be a better bet for most people.