It's all the driver and not the truck. Most of these vids you see are just people going for the 'wow' factor. They're not focussing on their driving / technical skill for the video. I know I have to hold the camera with one hand the controller with the other, which doesn't do wonders for my driving skill when I make the vids. When you drive it for real, you just have to learn to baby the throttle all that. Look at the way this B4 handles:
http://www.youtube.com/watch?v=e1a1kHW7eh0
http://www.youtube.com/watch?v=vklm5D6Z-HU
Or even this pede:
http://www.youtube.com/watch?v=lkjFzOQF-9E
Two different strategies at work here, the buggy is low to the ground and has a super-low CG, stays stable that way. Maximum traction on the rear wheels, and driven appropiately. Even so, it's possible to spin the rear wheels and flip, if you take it past the limit, but that limit is much higher than a high-CG MT.
The 'pede OTOH is completely newbie-proof on the grass (or dirt) b'cos of the way it slips and slides around. Despite the high CG, the anaconda wheels just don't have enough traction to tip it unless you do something really awful. The rear tires are out farther than the front, if you turn too hard it just understeers, if you accelerate too hard it just loses traction. I always let newbie friends drive the 'pede, they like the way it can fishtail a turn and it's real easy to keep upright.