well i think you have to take into consideration the numbers.As far as empty handed forms, You have a lot more people who were studing empty handed martial arts than weapons. The other reason that can account for diferences is that people did and do change kata for their own preferences. Odo sensei was known for adding diferent elements to kata quite often. So i think in regards to Okinawan weapons, as I posted earlier, we do see quite a number of diferences in weapons kata, however , with Japanese Koryu, there is a much stronger governing body that helps to prevent changes from happening. So yes I agree that if we look at emptyhanded forms and JAPANESE weapons forms, we dont see the diferences in their performance. However, with okinawan weaponry we do see a huge diference in their performance from school to school.