All valid points, Danlo. The reason I suggest we might have better control is because, as I understand it, the emotions of some people on the spectrum - especially people prone to overload/rages instead of numbness/shutdown - tend to be more extreme than average. So in growing up, they have to find a way to control it or else be unable to function in society.
Maybe it's because the part of the brain that handles emotion doesn't develop as fast. It's normal for a 3-year-old to throw a tantrum, but when a 15-year-old has the same emotional reaction, it's considered pathological.
Certainly there are plenty of non-spectrum disorders that involve extreme emotion (bipolar, histrionic, panic disorder, etc). So I don't think ASD people are the only ones. But people on the spectrum tend to respond differently to emotional stimuli than NT's. Something that would freak out an NT, like the death of a family member, might be shrugged off. But something that an NT wouldn't even notice, like flourescent lights or background noise, can throw them for a loop. When your natural emotional responses are out of sync with the rest of the world, you tend to get disapproval for expressing them, so you learn to control them to a degree that the average NT wouldn't find necessary.