If someone just randomly asked me to define "RS Types," I would in a very general, broad-based way say:
"People who are interested in the world, do some (or a lot) of research before their trips, are somewhat value-oriented (but maybe not always, and are somewhat better educated than the general Joe on the street in America."
Then, I would also add that those individuals may not (or maybe they have) have done a lot of travel in Europe. I think (again in a broad-based GUESS way), I think Rick Steves attracts both the newbies to European travel and the very experienced (who value his knowledge and the knowledge of fellow travelers, like on this Forum). There is no way any of us can know everything!
In a very broad-based way, I think the Rick Steves' type traveler MIGHT be more physically fit than some other travelers from the US to Europe.
Again, broad-based generalizations -- ALWAYS many exceptions.