I enjoy watching RC helicopter stunts like these. Many RC pilots are very talented, executing barrel rolls and other inversions.
How come we don't see these kind of displays at airshows?
First off: I'm not a pilot.
I believe there are two additional issues here:
There is no pilot in the RC helicopter. The forces exerted in some of those maneuvers look pretty extreme, I highly doubt even the most well-trained aerobatics pilot/astronaut/fighter jock would be conscious longer than about 2 minutes into the video you posted. I'm not even sure if they would be able to survive that.
Scale. All sorts of weird things happen when you scale complex systems up or down. (A famous example is the square-cube law: when you scale a structure up linearly, it's area scales as a square, and its volume (and thus weight) scales as a cube. So, an ant that is 100 times bigger will have feet that are 10000 times bigger but will have to support a weight that is 1000000 times bigger.) For example, the airframe of the RC helicopter is much stronger in relation to its size than it is on a real helicopter. Also, RC models (not just helicopters) are typically ridiculously overmotorized compared to their real-life counterparts.
There just aren't many helicopter aerobatic pilots around.
There is one I know of: Chuck Aaron he can do the typical maneuvers in a specially modified helicopter.
As ratchet freak mentioned, it is simply not common. Why, you ask?
Airplane aerobatics? Calculated, practiced, somewhat risky, entertaining.
Helicopter aerobatics? Closer to a death wish than airplane aerobatics.
The aerodynamics of helicopters are more complex (think fragile). There aren't as many people willing to do it.
First off, the reasons you don't see real helicopters performing literally like that model are that it's impossible to get anything like that power-to-weight ratio on a full-size machine and also because the pilot would black out from the ridiculous G's being pulled.
As for why you don't see a whole lot of... less ambitious acrobatic flying in helicopters, it's possible that certification is an issue. For example, the British Army Lynx display includes rolls, loops and even back-flips. However, I distinctly remember commentary at an airshow I attended saying that, when the Lynx is retired fairly soon, its replacement won't be certified for any kind of acrobatics.