If I remember correctly, they changed that twice.
I'm sure they changed something when they did the special edition version, then changed it again for DVD.
I think the point they are trying to make is that Anakin essentially died when he was young, so he reverts to the earlier incarnation, where as Yoda and Ben stayed young.
I also think it was just a way of linking the two trilogies together, just like when they shoehorned the two droids into the newer ones!
