Like a lot of things thai ( from their women to their language) it isn't straight forward to western ways but in thai idealogy would be perfectly logical. Good point on the explanation of fouls tony. An old thai coach of mine said no tripping then one of his fighters tripped me I said "foul!" He said " no foul because beautiful!" I laughed and thought typical thailand just accept it. Body kick carry far more inertia ( moving weight is the word I'm looking for if inertia is not correct) that is clear to see when holding pads therfore is going to cause more effect surely. A kick will knock you flying if hits right a punch can spark you but wont move you half way across the ring.