They've changed the design from a plug that attaches perpendicularly into the laptop (and has a serious strain point that is not adequately engineered around) to one that plugs in "parallel". http://en.wikipedia.org/wiki/MagSafe

This likely prevents strain by removing the probability that the cable is pulled at the strain point. It also looks cooler.

Only downside is that it doesn't untether easily; it's that the selling point of MagSafe?