Lethwei, muay khmer and muay thai are all very closely related. The Thai fighters wear gloves because they can afford them. Lethwei fighters still use rope and gauze to protect their hands and there is the use of headbutts. Also in lethwei matches there are 2 referees, I believe one from each camp. Other than that, they are amazingly similar. From what I have seen it is just different flavors of the same sort of thing. Like the difference between Syrian Arabic and Jordanian Arabic. It's still Arabic just a little difference in expression.