At some point, it's probably as much a money saving measure as anything--plus all electric sounds high-tech to some. I think it's also a bit misleading, as diesel fuel is not electricity, and is very necessary to the operation of the coach.
Certainly, once you decide on a residential fridge (which is presumably a rather popular option) and add in an AquaHot or similar for heat and hot water (also presumably a rather popular option), it starts to make little sense to build and carry a propane setup solely for the stove. Simplifying the construction and marketing it as more upscale is good business sense.