Have been a martial artist and a part time actor I can tell you there is several factors that come into play on this subject. First martial artists on screen do the scene over and over again, sometimes a scene 5 minutes takes a month to film. The camera angles are also carefully crafted to put the star in the best light. Often stars go on a quick diet to look sharp. Which adds to the film "coolness" After the fight scene the are ofen covered up and during the shots their bodies arent shown their ripped quality fades. Remember Stallone in Rocky III he had a bodybuilders body at 3% fat. No heavyweight boxer in the world would reduce their bodies to that ripped condition. It simply wouldnt hold up to the constant pounding a boxer goes through. Most stars that are martial artists in real life perform feats that only can be done on film. They are employed and often have to do what the producer and director say regardless if the action or movement would be considered impractical. Jet Li, like Bruce Lee is a fine martial artist. Bruce even performed basic movements in his films due to the fact that advanced techniques would confuse the audience. As for the UFC they too are at what they do, however placed in a movie setting how many of us would pay to see a guy sit on top on another and pound him for five minutes until he submits. Each person provides us with entertainment lets enjoy them for what their worth.