You're not alone in thinking that, and there are some studies which seem to agree.
Fans of GURPS, or anyone looking to hear it in action should check out the podcast "the film reroll" (if you haven't already). They play through films as RPGs using GURPS and it's fantastic! They even had the creator of GURPS on once as one of many people playing Leonard in Momento. Also, there are absolutely no adverts.
I haven't done too much research into ADHD (which I don't have) but if it's anything like autism (which I do have) then it may well be that it's just massively under diagnosed in people who aren't rich, white, boys. I know they aren't the same but that's certainly the case for autism, and there is a high rate of co-occurrence between the two.