I owned a 2006 ADV950....and then a 2012 990 SMT and now a 1090R. In between or at the same time were a 300EXC (best dirtbike EVER!!), a 530 EXC and a 690 Enduro.
The progress in the V-twins in terms of rideability, fueling/power delivery, maintenance, and reliability are stunning. Suspension and handling have stayed top shelf all along. The India-made tool kits of the recent models are cheese in comparison to the Austrian made ones.
Ewan and Charlie would have run out of gas on the 950's constantly. As much fun as it was to ride it was SUPER THIRSTY. So was the 990, but that was likely my fault, at a sedate pace it....nah forget it.
There were a couple other things that made long rides less than comfortable on the 950 too, so I think they were probably better off on the GS's.
Plus Ted Simon rode an airhead GS for Dreaming of Jupiter so maybe they wanted some connection/similarity to a serious RTW adventurer-traveler.
In my opinion, Ewan and Charlie's ride pales in comparison to both of Ted Simon's trips, but to be honest all their travels are well beyond all I have done or ever will.