I think it's just the design. Where the cables exit the brick they are prone to strain -- the connection wire comes straight out. When you put the connector away, no matter how you do this, there will be some strain on the cable at this point.

To some extent all power bricks will have some problems like this. I just think that the apple power supplies are particularly poorly designed. I've had a Dell and a macbook pro. The bog standard power supply on the Dell lasted 5+ years of daily use. The apple connector -- which I cared for more than the Dell -- lasted just over a year.