If you purchase something in bitcoin, there's a 2-4% fee tacked on as well. Try to buy something in bitcoin at tigerdirect for instance. Look at the fiat price and then compare it to their BTC price, converted to fiat.
Bitcoin enables vendors to offer the same "cash discounts" as done with cash transactions. The two gas stations closest to me offer a "credit" price and a "cash" price. The cash price is cheaper. If more people use bitcoin, we will see vendors do the same and offer discounted prices in BTC.
The thing to remember is the wording is all marketing spin. These gas stations are not offering a "cash discount", they are really charging a "credit surcharge".
But people don't like to pay extra surcharges, so marketing just calls the real price a discount.This reminds me of what happened when coke tried to enable vending machines to charge different prices depending on the temperature. What they really tried to do was raise the price on hot days and charge more, but that turned people off. So instead the vending machines were programmed to say the new higher price was the real price and on colder days you received a discount (back to the regular price).
People like discounts, they hate surcharges. The key for bitcoin is to expose how everything else prices in a surcharge, but bitcoin offers a discount.