In college I took a cognitive science class by a professor who researched human memory systems, and had done some studies of autistic patients. He had a particularly good explanation of how these autistic people develop such phenomenal capabilities.
He argues that there is nothing superhuman or magical about them. If a “normal” human being were to spend as much time, energy, and focus as they do on developing certain abilities, such as the ability to draw from memory or to perform multiplication in your head, the person would be able to achieve the autistic’s level of skill easily. He had numerous studies that lent support to this statement - studies primarily involving measuring how much devotion (time, effort, etc.) an autistic patient spent on their task of choice, measuring the devotion of a healthy practitioner of that task, and comparing relative proficiencies in said tasks versus the degrees of devotion. Autistic patients did not come out on top.
However, part of being a “normal” human being is the ability to tell when you’re devoting too much time and attention to something trivial or insignificant, or simply spending energy on one thing when you could be spending your energy better elsewhere. The mechanisms that trigger such reallocation of energy in healthy people include boredom, frustration, fatigue, or sometimes simply a “little voice” that makes you step back for a second and ask yourself, “Wait, why am I doing this?”
Being autistic means, in part, lacking these mechanisms. Autistics are able to develop such skills, in other words, because they don’t know that they don’t have to. :)
Like FR addiction?
I’m afraid that it takes some of the magic out of it, and many people (parent-advocates) think that this explanation makes these people less special, and therefore they reject it. There is far too much political advocacy and too little science to the modern treatment and management of autism.
I'd look at it a little differently. We "normal" people aren't as focused on one thing not because we chose it, but because we can't help it. We want to eat good food. Walk in the sun. Find love. Have and raise children. All those distractions. "Normals" can become obsessively focused, but not to the degree Autistics can; it's the difference between trying to ignore something and not seeing it.