Okay Barrett, excellent question, and I will try & explain this fascinating situation as best I can:

During the Outfit's arguable peak (the Giancana period), it was ran as one family. Sure, it was much larger, & there were more crews than the current 5, but no matter what happened, Ricca/Giancana had a final say in pretty much everything that took place. This proved detrimental, obviously, to the Outfit's longevity & well being, so during the mid to late 70s, Aiuppa/Cerone/Accardo constructed a different type of system, one where each crew was separately insulated and an entity unto itself, a "family", if you will, with Cicero & Elmwood Park being the two heaviest of these families, and Grand Ave, Chinatown, & the Heights being the three sub families, which continues to this day. Aiuppa also implemented people he trusted at the head of each family. In doing this, he allowed the outfit much more breathing room and insulation. LaPietra, Lombardo, Cerone, etc were all technically beneath Aiuppa & his Cicero family, but ran their own crews as if they were separate families entirely. IE, if you were/are a Chinatown soldier, you have no business fraternizing with an Elmwood soldier. You deal with members of your own family & answer to your boss. Likewise, the boss of, say, Grand Ave doesn't have to get everything okd by the top boss. He controls is crew as if it were his own private family, obtains much more power/control/responsibility. Families were in turn almost encouraged to not associate with members of other families, very similar to the NY set up, obviously on a much smaller, more secretive scale. Hope that helps, any other questions, please ask.