If you are talking gas engines, the A & the C will be the same. Tranny & rear axle gearing may differ a bit, though. The diesels used in the bigger pushers are in an entirely different class.
Typical mileage varies by type of use. Typical weekenders probably run around 3000 or so per year, while those who can manage longer vacations run more like 5000-7000. Snowbirds, long timers and fulltimers are more likely to be in the 6000+ range. The RVIA merely gives 6000/yr as typical for all RVs, but it's not known how they come up with that. I doubt if its more than conjecture, since there is no reporting system nor any regular owner surveys.
I don't think that "expected" vs actual has much value anyway. Wear & tear is wear & tear, whether it is average or above/below average. The real question is whether the one you like is in good condition or not, and odometer mileage is just one of many indicators. The gas engines designed and built in the past 15-20 years have a very long service life if given even halfway reasonable care.