I recently purchased a VPN service using Bitcoin and they gave me a very nice discount that would have more than covered any costs associated with procuring the BTC.
Imagine if Amazon starts accepting Bitcoin and offers a mere 10% discount

Those discounts are promotions. They are for publicity and to get people to use bitcoin on the sites. They are not permanent discounts which come about from accepting bitcoin. The merchant will save about 3% from card fees but the customer will pay that to buy the btc.
I just want to see a solution for this problem. I know it wouldn't exist if we were all using bitcoin but to get there we need to remove volatility and to remove volatility we need to more adoption. Catch 22.
I am not saying that bitcoin wont have any value. It will be a store of value like gold is. It will be better to hold bitcoin over fiat for the future because of inflation.
International transfers, some black market stuff and a store of value seems to be where BTC will be in the future. It wont be very common unless there are real incentives. And right now no one has provided any. So BTC is Gold 2.0 and not a common currency.