Maybe the people who think the punches are different are only looking at the fully extended karate punch done in front stance and can't see how it developed. Isshin ryu punches are vertical so I guess you could say they are different than boxing punches but both systems (boxing/karate) throw a punch the same way. push from the legs, rotate the body, rotate the arm, hit with the knuckles. Both the same. Only boxing's wild haymakers are different from karate punches. It's possible that the rules of a certain karate style allows for the hands to be lower, for example the rule no punches to the face, but the punch still generates power the same way. IMO