I've been reading an interesting discussion on the blog A Grand Illusion, which began by asking what's wrong with wanting a cure if someone feels that they can't do what they want to do because of their autism. A commenter posted a snarky reply along the lines of "get over yourself, there are plenty of starving peasants living in huts who are much worse off than you." By way of rebuttal, the next few posts had to do with indigenous cultures and how happiness is perceived in different places across the world. Global surveys asking people to rate their level of happiness have shown that peasants living in dung huts in isolated villages feel significantly happier, on average, than the urban poor in wealthy countries.
Happiness, it seems, is more about cultural expectations than it is about material wealth in the abstract. When people feel that they have as much as the others in their society, they are happy; but when their culture dictates that they ought to have something else, they're likely to complain about whatever they don't have and to see themselves as unfairly deprived. People tend to take for granted many things that make their lives easier—such as electricity and running water—if everyone around them also has these things, and they don't feel happier because of having them. On the other hand, peasants who have never had such conveniences in their villages don't have any reason to think about it.
I would take this point even farther and say that it effectively answers not only the snarky commenter, but also the original question of why autistic people have different levels of satisfaction with their lives. There are some who feel like the urban poor in the surveys, believing that if they weren't autistic they could accomplish more in modern society. Others have an attitude more like the contented peasants, never having thought of themselves or their autistic family members as lacking anything in particular, and taking offense when those who don't share their perspective find fault with their way of life.
When people have different cultural expectations, arguing about how they ought to feel isn't likely to change anyone's point of view. As with any such differences between groups of people, it's often more useful simply to discuss what they feel without being overly judgmental about it, while working toward a more constructive mutual understanding.