you didn't read my post. the cross over of the feet is an effect not the cause. it's an illusion.
again, if you left round off...the athlete will 'hop' on their right foot during the hurdle phase (assemble). as they hop on this foot and swing up their right arm there is a natural tendency for the body to slighty turn to the right. when they step down their body lands in a position that is already turned giving the 'appearance' that they have crossed over. it's an illusion, understand? the body was turned and crossed over BEFORE it came back down to the floor after the hurdle.
so, you keep the right arm at about parallel. this can be played with and tweaked. this keeps the right side of the body 'shorter' than the left and 'counters' the subtle tendency of the body to slightly turn to the right.
and Geoff, what you experienced is not a coincidence. this technique helps some kids more than others. but where you will really see the 'correction' is when they yurchenko. you see, the faster they run and the further the run down the runway is where this "twisty" round off can really rear its ugly head. keeping the arm in a certain position improves the performance of the round off. in many cases, you can take a terribly degraded round off and make it near perfect.
and as you pointed out, diego as well as several other olympic gymnasts perform the same technique. and they do it for a reason. it is NOT because there is something wrong with their round off. this is equally performed by gymnasts doing round off beam dismounts and front handspring front twisting skills on floor.