To be fair, you could easily see this as one of Amazon's "features", much like Zappos. Everyone orders from Zappos knowing that they can not only return shoes for free, but that it is usually encouraged to buy several and return the ones you don't want.
While Amazon isn't quite so blatant about that "feature", their incredibly awesome customer support, zero-hassle returns encourage this kind of behavior...effectively making it a feature.
I often wonder if Amazon's acquisitions of Zappos and Quidsi (Diapers.com, Soap.com, etc.) are simply to experiment with different "features" without risking changes to Amazon.com.
While Amazon isn't quite so blatant about that "feature", their incredibly awesome customer support, zero-hassle returns encourage this kind of behavior...effectively making it a feature.
And to be honest, it's an awesome feature.