I find that kind of thing fascinating (and very disturbing!). Those Russian kids seem to be less bothered about what they are doing than we are. It's always possible that they were drugged out of their brains, but I've known people like that with no apparent fear of heights. I've always been bothered by them, to the extent that I got stuck up a tree once because I was too scared to swing off a branch to get down. I was only about 7 feet up!
When I was about 9 years old, one of my friends climbed up a large tree and poked his head out of the top of it, while balancing on a slender branch. He must have been 45 feet up and would almost certainly have fallen to his death if he'd slipped or the branch had broken. It freaked me out; he found my reaction funny. A friend of a friend did the same thing, but in his case the branch snapped and the fall killed him. Also interesting - the friend who witnessed the fall was only upset by it for a few hours, and then just shrugged his shoulders and got on with his life. I'd have been completely traumatised by it. That friend went on to race motorbikes when he was older. He gets bored easily.
I think each person has their own natural psychological sensitivity level. Those with low sensitivity need to do outrageously risky things to get their kicks. More sedate people (such as myself) get plenty of stimulation from everyday life and are horribly over-stimulated by things such as exposure to big heights or fast driving. Some people are hyper-sensitive and are frightened to do very much at all. I'm cautious by nature, but I will still descend hills at 50 mph on my bike so I'm amazed by how slowly some people go downhill. Panic braking to 15 mph on a 5% slope - come on!
What interests me is how resistant to change the natural sensitivity of a person seems to be. Low-sensitivity people need to be on the go all the time, desperately seeking excitement. One of my nieces is like that. She won't sit quietly for more than about 5 minutes. Soon, her phone will be out, or she will jump to her feet and start marching up and down while she is talking. She can't understand how I can sit for 12 hours a day working at a computer. In fact she didn't believe me when I told her that I once spent 5 days indoors by myself averaging 16 hours a day at the PC.
The low-sensitivity people of this world are the people we need to fix high level radio antennae or clean windows on the outside of skyscrapers. We more sensitive types are good for tasks that thrill-seekers would find boring.