It's a comfort thing. The more comfortable you are with your riding relates to the more relaxed/aggressive you'll be in your movements. Emulate the things other riders do all you want, but don't overthink it. Does that make any sense? Those guys are using one hand in that situation because they are comfortable, there isn't a reason to do it that would make you a better wakeboarder. I ride with a guy who does this. You can tell he's thinking more about dropping and replacing his hand than the cut he's about to make into the wake. I don't want to sound like a douche, but it shows in his riding. That's overthinking, ride and have fun, worry about how you look after you've got something locked in.
As far as their edging? They are still using a progressive edge, only more aggressive. You said it your self: start the edge, crank down, speed into the wake. It's the same concept as taking a gradual and linear edge, but from what you described its balls to the wall. Do what your comfortable with and go from there.