You are assuming people aren't smart enough to convert USD to BTC. If I need to buy a computer and can save 10% value by buying from bitcoinstore with BTC over USD at amazon, I'll just buy some BTC with USD and then make the purchase. I haven't bought a computer, but I have done this exact thing for other items from a variety of bitcoin stores.
Not that I want to be the one to pee in your Cheerios, but you do realize that a lot of people think paying 400% for a TV at a Rent-A-Center is a good deal because it's the only way they can fit a 60" Samsung into their budget without a line of credit. The average Joe Schmoe is just fine paying 150% for a PC upgrade at Best Buy because they don't even know NewEgg exists, let alone how to swap a hard drive or a video card.
I think you're really overestimating the average user.
As the prophet George Carlin once said, "Think of somebody you know that you would consider to be of average intelligence. If that's average, then realize that half the people in America are dumber than that."