This is especially true for online purchases. Right now the entire ecosystem of Amazon / Paypal with banking services directly linked or through credit / debit cards, works pretty flawlessly. You can buy anything on the internet immediately with real money linked to FDIC insured banks running through two huge easily trusted middlemen, with little to no setup other than having bank account.
You are clearly an American :) Also, Amazon would approximately double its profit if it were not forced to pay the 2% markup on credit card charges. And before you criticize coinbase for their 1% conversion fee circle is here with 0% :)
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...
