Actually I disagree with this, hence why fighters are starting to use more front kicks (two knockouts recently). Precisely because pretty much all MMA fighters train against Muay Thai style kicks not Taekwondo style kicks. This is why fighters like Cung Le, Anthony Pettis and Ben Henderson have done so well - their kicks are unorthodox in comparison to the majority of MMA fighters. Even Lyoto Machida has success with his Karate-style kicks because they are different to the general kicks that MMA fighters are used to dealing with. I'm still waiting for someone to land an axe kick in MMA! That'll be awesome!