How don't they? They have people who are in charge of people and people who are responsible to others, yes? I just checked to make sure I wasn't going crazy here:
"A logical element or segment of a company (such as accounting, production, marketing) representing a specific business function, and a definite place on the organizational chart, under the domain of a manager. Also called department, division, or a functional area."
http://www.businessdictionary.com/definition/business-unit.h...
It's a term that seems so totally generic that I feel like you have to work really, really hard to find an organization at scales far, far below where Apple operates to find a company that wouldn't fit that description (Valve?)
But that misses the point -- the point is that Apple has SOME existing organizational structure around "selling consumer electronics," and that an Apple-purchased Occulus would likely fall into that structure. I don't think there's any evidence of a company that Apple bought and let run on its own for an extended period of time, is there?