I have done a few of the above listed.Almost anyone can do them provided that they are in good physical condition and do a little practice. Most of the "tricks" do require concentration/focus. They are good visual examples of such. As most if not all martial arts require conc/focus and discipline as well as good body/strength training and conditioning, there is nothing wrong with these feats. The unbendable arm is a demonstration of ki or chi flow,which everyone has. The breaking of blocks/bricks is a little more difficult, not everyone can do it. Again, practice and hardening of the body are required.