I i remember right, it was a change that happened when drops were getting away from the benotto and cloth tape bars going to the cork base.
If its Cork base or any of the padded bar tape then they say go bottom up
if its a benotto or a clot tape then you can go top down.
It basically has to do with the cork tape being as flexible as it is and stretching. so you wrap in the direction that the hand would move to tighten the tape not loosen.