That's the rationale in those books at least. I think I always subconsciously applied it to the Harry Potter books, too.
I almost mentioned it, but then someone posted something that reminded me that in HP it was said that the witch trials and such were singularly ineffective at finding actual witches, since they could cast a simple spell that would, for instance, render them invulnerable to flame while they were being burned at the stake. So unless that was some kind of white-wash to keep from traumatizing the kiddies, and when Hogwarts students got older they found out how dangerous muggles could really be, the Dresden explanation can't apply to the other wizard called Harry.