Amazon is selling a 45watt MacBook Air power supply for $20 less than Apple. The title is interesting: Amazon.com: Genuine Apple 45W MagSafe Power Adapter for MacBook Air A1244.
Why is the title interesting? Because of the word "genuine". Remember the old wisdom - "people's republics" are always tyrannies. Products that claim to be "genuine" often are not.
This particular product could be genuine. Not so the "apple" cables sold on Amazon for $2 instead of $20.
There's a lot of counterfeit Apple gear for sale on Amazon.
Amazon is increasingly a competitor with Apple.
I'm sure those two facts are not related.