See, the Rhino's "cylinder" is not a cylinder. It is a hexagon. Yet, what are we supposed to call it?
If we call it a hexagon, no one will know what the hell we are talking about. As a part of the revolver it is, in fact, called the cylinder, but that's only because just about every revolver's rotating chamber mechanism has been cylindrical. No one will think us wrong for calling the Rhino's hexagon a cylinder in the context of revolvers, but it terms of geometry, it is wrong to call it a cylinder. Therin lies the aneurysm I'm about to have.
We could call it a "rotating chamber mechanism," which would be accurate, but awfully clunky. And, going forward, what would you call, say, a J-Frame's cylinder, which is actually a cylinder? Do we change everything because of a single (for now) anomaly? Do we maintain the status quo at the expense of accuracy because that's always easier?
The answer is: we drink. A lot.