It is not the purity of the definition but the abuse of the definition. You hit on one such difference right in your message about fixing leaks. That is generally a whole discussion typical of stick built Class Cs that are generally not true of Class Bs. I am not interested in reading about the repair and maintenance of rubber roofs for instance that could come up because someone with a stick built Class C thinks he has a Class B. OK, that is just one little example but to me they are entirely different other than someone saying some can be just as short or shorter and that is pretty much it.
A Class C (or B+ if you wish) is taller and is wider than most all Class B vans. They generally have full baths with separate shower. They are generally roomier. But then owners come into the Class B forum and tout those advantages at the same time pissing on Class B owners for putting up with their limitations. They are blind to all the sacrifices they compensate for and don't realize they are doing it. I don't think they realize how much touring freedom they gave up. I get together with Class B and Class C owners on a social basis. I've seen the change of habits and concerns those with Class Bs going to Class Cs have gone through. I've seen some come back to Class Bs on account of that. I've seen some move on and be happy about it. People do go through changing stages, desires and routines. That's why there are Class Bs, Class Cs, Class As, 5th wheelers, trailers, tear drops and tents.
They have a B+ Forum. I don't see Class B owners going there and bemoaning how too tall or too wide or too difficult to drive everywhere a Class B+ is in that forum. Hey, but we will be glad to do it here in our house. :)