Mythbusters is stupid entertainment. They used modern wood shaft material of questionable quality. That influenced the results they got.
With modern shaft material, a complete robin hood is real hard to do, because of the uneven angles of the grain etc.
In the middle ages, raw shafts were usually split out of a piece of log and then reduced to a round surface. That's why long-fibered wood was used a lot, like fir or ash. These woods split easy into small+long+straight sections. This minimizes grain-run out to an absolute minimum and ray and normal grain is alligned correctly. The only thing needed now is another splitter absolute center in the shaft....which is your arrow with a broadhead on...
Another reason quality wood shafts are expensive, becasue they try to have the grain as parallel as possible using saws (instead of splitting). This results in a lot of excess waste wood, which must be bought by the manufacturer and what makes his product more expensive...
Howard Hill probably buildt special arrows to achieve those shots and I bet he split wood into small sections and then reduced em ect.