Amazon will accept your credit card payment and won't accept your Bitcoins, which is a pretty good indication of which payment method they feel is more hassle than it's worth.
Fortunately Overstock does accept Bitcoin already[0], so it's a pretty good indicator that there are other considerations too. Also, you can use Gyft[1] to spend bitcoin on Amazon and even get a discount - if there's enough business that another company can support itself on users you are not catering for, then there's definitely a business case...
[0]: http://www.overstock.com/bitcoin [1]: http://www.gyft.com/