Diesel is nice, no doubt. But unless you're running fast in the mountains, carrying a big load or putting 10K+ miles a year, it can be overkill. Most people don't need the the added expense. Now if money were no object, sure.
A 28' Class A is relatively light. I've pulled 2 bikes (or a small boat) through Western NC mountains without any problem (32' Winnie with 454 EFI). Slower than a car? Yes, but still way ahead of a loaded semi. Brakes are much more important than power.
