have also seen many observations and references that state that role-players tend to be of above average intelligence.

Weather this is because role-playing encourages intellectual development, that these people tend to be attracted to the games, or that the industry is just being conceited is unknown. I haven't seen any research on this topic.

My personal opinion is that the former applies: that by forcing players to come up with creative solutions to problems the game encourages creative thinking, develops problem solving, and mental agility.