Yes, self discipline can be a problem, and as our son has gotten older (and we stopped the medications about 4 years ago) that is the continual struggle.
BUT, with regard to video games it is a different type of stimulation. And it is quite common for ADD/ADHD diagnosed kids to be able to play for hours. The research is out there.
Come to the cicus and watch monkeys jumping through burning hoop and then watch the experts try to make convoluted explainations on why their brain disorder diagnosise is selective.