I would not care to be without a built-in ladder. Maintenance and cleaning are frequent enough needs on an RV to make it very handy indeed. (Cleaning may be something as simple as sweeping off pine needles.)
My last camping trip, I stopped at a strip mall to do a little bit of shopping and happened to notice that there was a six or eight foot long piece of branch that apparently had fallen onto the roof at the last campground and was now tagging along for the ride. There was no damage or anything, but it wasn't really something I wanted up there (and certainly didn't want to have suddenly fly off and cause a hazard to anybody who happened to be behind me). Having a built-in ladder made removing it and checking for possible damage a trivial job.