I get all my advice of my mom.. she had one heck of a stong willed child (and she's not suprised that I have 2 of my own)
At lot of the techniques we use is to remove the parent giving order to child structure. While its not a total democracy, both our kids do get some choices in what they do. We also work alot with consequences as punishment as time outs rarely if ever work. For choices, they get to chose the clothes they want to wear, the food the want to eat etc.. Though I usually try to limit those choices. Sometimes when Alex still refuses within his given choices and wants something else (like wearing pajamas to school) he gets to as this helps him learn that the choices he makes have consequences and sometimes those aren't very fun or nice. Several times he refused to put on a jacket, took one step outside, turned around came back in and put his jacket on so I know he gets it.
The other thing we do is ignore tantrums. I would literally walk out of the room when either child would throw himself on the ground and refused to give them the attention they wanted. This works really well with Mason, but Alex hated it and would still tantrum for long periods of time when he was 2-3 years old (4-6 hours easy so times). So in addition to ignoring him, we had to help him learn some calming techniques (blowing clouds out of his mouth, washing his face with cold wet wash cloth) whihc helped drop the tantrum time.
As for time outs, we call them breaks and they aren't for punishment but rather for the child to regain their composure. They are not for set times, but rather however long he needs to come back and be a nice person again. Mommy and daddy also get breaks and sometimes Mommy and Daddy get child breaks (when we basically confine the problem child to their room with the use of gates, no punishment they are free to play etc.. just mommy and daddy need some time away from the child(ren)).
Its very hard not to lose your temper with kids like these, but one thing that helps me is they aren't doing this to spite you or to be mean or to make you mad, but rather its a form of learning, building confidence, and expressing themselves. Also, the benefits later on in life do exist for people with these types of personalities.
As for who this occurs in, well I was a full term baby with 0 complications and I am easily described as strong willed, both my boys fit the description, and I have met other people who have had perfectly normal pregnancies who's kids fall in here too. It may have something to do with overstimulation, but its also a personality trait, some people simply by personality alone are more likely to buck the system and try to do everything they can get their hands on.