Couldn't a partial explanation for this be that those in higher paying jobs (i.e engineering) are more likely to take their children to specialists to be diagnosed?
And expected to maintain a certain degree of clinical detachment. If they were basing their parenting relationship on doctor-patient relationships, I'd not be surprised if they had a high rate of autism in their kids.
Not that I'm saying they do, just that if that were the line of logic one were to go down.