The 45W MagSafe 2 Power Adapter features a magnetic DC connector so if someone should trip over it, the cord disconnects harmlessly and your MacBook Air stays put safely. It also helps prevent fraying or weakening of the cables over time. In addition, the magnetic DC helps guide the plug into the system for a quick and secure connection."
Highlight in red is my own emphasis. Unfortunately, the MagSafe 2 (2012 models) was too weak. Many customers reported that a slight brushing will detach it. This created a huge dissatisfaction among the community. We all want the MagSafe 1 back.
So, with the release of the new intel Haswell-based MacBook Air in mid-2013, Apple made some slight tweak to the MagSafe 2. They made it stronger, so that it didn't detach that easily.
I have a brand new mid-2013 MacBook Air 13" and I found, to my dismay, that the MagSafe 2 is just too strong. The magnet is so strong that I can lift a MacBook Air with it:
The product is not working as designed nor as advertised! I want my money back!