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?
I got my macbook pro last november with the new connector. The MagSafe connector is already broken. I attach/detach it maybe 3 times a day.
Seeing everyone I know that has a macbook have his/her adapter fail, not getting a replacement and then having to buy a new one for 80 EUR I took extra care. Still the cable broke inside the connector!
I've never had this problem with any other device or notebook. Seriously, power adapters should be simple and just work - except they don't for macbooks.
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?