the importance of the accusation of Jane Shore and Elizabeth Woodville of witchcraft in withering his arm?

Answer 1

Richard III, King of England for a short time, has been painted by various writers as a villain and has, accordingly, been described as a hunchback with a withered arm. He may, in fact, have had one shoulder slightly higher than the other, and there may have been something wrong with one arm - but not to the extent that has been characterized by, for instance, Shakespeare.

Jane Shore was a mistress of Richard's brother, Edward IV; Elizabeth Woodville was Edward's wife. It was John Morton, Bishop of Ely and then Archbishop of Canterbury during the reign of Henry VII (who succeeded Richard III), who was an enemy of Richard III and who may have been the source of the accusations of witchcraft.

Though Richard was well liked in his territories in the north, even in those brutal days child murder was viewed as appalling - the disappearance of the two little princes in the Tower of London. Henry VII had to consolidate his position as King after the Battle of Bosworth, and many stories abounded detailing the crimes and sins of his predecessor; even the saintly Thomas More painted Richard as a deformed hunchback. You can also read the Wikipedia article:
http://en.wikipedia.org/wiki/Richard_III_of_England

Where we wouldn't countenance accusations of witchcraft today, in the 1400s they would have been important and believed. Richard was painted as a villain, and villains would generally show their characters in physical attributes. Remember, Elizabeth was the mother of the two little Princes in the Tower.

Answer 2

Both were in the Court of Richard III

Found no reference to witchcraft..... or the 'withering of the arm' for either however.

Both were accused of many things, Jane specifically being accused of "promiscuous behavior by the King". Seems he thought that her walking through the streets of London with a lit candle in the night attracted unwanton male attention....