As someone who gets shocks all of the time, i find it strange that one place i never get a shock is getiing out of a car.
Part of your explination is correct, but only one of many. Static build up from friction moving out of a car with nylon seat coverings is a factor. So is the clothing worn by the person, as far as i understand it, women are more prone to shocks from cars because they "tend to" wear more brightly coloured clothes which are more often made of a synthetic material thus creating more static.
I agree with almost everything you say. You are correct that it takes more than just seats. I said that leather seats do not produce shocks. I should have added that leather pants do not produce shocks either. It is the two materials rubbing against each other that cause the shock.
I disagree however with "only one of many." There may be many explanations, but this one is correct.