RST, would you like to do a non-scientific experiment?
I will give you a quick programming problem using recursion and I will give you any help you need until you can solve that particular problem.
Then I will give you as much time as you need to study up on recursion until you are sure that you can solve any simple problem on recursion (the point is that you master recursion, not just learn to solve the one specific problem).
Then I will give you an equally simple, but different, problem using recursion to see if you you were able to pick it up.
My belief (and the articles in question support this) is that only a relatively small number of people have the mental capability to master recursion, not because it takes a bigger brain, but because it requires a specific type of abstract thinking that not everyone is built for. And I believe that no amount of effort will give someone that ability. You either have it or you don't.
It is funny that I have accepted that I will never be 7 feet tall or even 6 feet tall, and I have accepted that I will never be able to run a mile in 5 minutes. Some people are born with athletic ability and some people aren't.
Why is it easier to accept this truth with physical strength than it is with mental ability?