I don't know about the rear end, but it is known that dealers have their own recommended maintenance outside of the what the factory wants. Theirs is based on dollars and can include such things as a Transmission flush, engine flush, differential oil replacement, radiator flush, and on and on. My bottom line is it is a factory recommend service I'll do it; if it's a dealer recommended service I won't. Outside of money down the tubes it has been know that the dealer charges for the service, but the service is not performed (can't say whether it is a lazy mechanic or a corrupt dealer), but most people wouldn't even know if the service was performed,

I'm still looking to see if the factory recommends a rear end fluid change...