I want to buy a pair of trainers that typically cost $80 USD, back in July I could have purchased this with 1BTC. So lets say today that same vendor has them marked at 1BTC or $80 USD, if I paid by BTC my trainers now cost over $800!
So the problem is for the customer not for the merchant. That's why so many people are hoarding instead of buying right now.
If i was a merchant i whould love to do every single sale in bitcoins.