The main difference between C and super-C is marketing. A super-C is usually used to describe a class C that's built on a heavier duty chassis than the typical van-derived chassis used.
The class of the motorhome has absolutely no bearing in itself on what sort of license you need, by the way. It only describes what sort of a chassis the RV builder started with, and how much of the outside body comes from the chassis and how much was added by the RV maker.
A class A starts with a bare chassis, and the body is entirely added by the RV maker. A class B starts with a cargo van, and the RV is built inside the van (possibly with the roof being raised/added onto). A class C starts with a cutaway cab chassis (or I suppose a chassis cab), and has the RV part built onto the back. Some things don't quite fit as well as one would hope into this taxonomy, and the toter is in many ways one of them; it most closely resembles a road tractor with an oversized sleeper, rather than a traditional RV. A school bus or motor coach conversion might be another; logically it would seem to me they should be class B's, but nobody really considers them as such.
