They accepted Bitcoin by allowing it to be used as a currency for purchase. If that payment is then converted by a 3rd party, then that's not the consumers responsibility, that's the product supplier.
It could also be further argued that they do accept Bitcoin as they refund in Bitcoin.
If I went to amazon.com right now and used my credit card (in Thai Baht) and bought a TV. Then 5 days later no TV and they give me a refund. Lets say in the 5 days Thai Baht goes up 400%. Do I get the Baht back?
I kinda doubt it but I really don't know.
I don't know either.
If I get some free time today I will call AMEX and ask the inverse question. (Purchase on my us card in Baht that is refunded)
That is exactly how it works with credit cards.... I live in the UK, if I buy an item in NYC for $ and it breaks and I get a refund under my insurance I get the $ value back.... if the £ has moved in my favour then it is my gain, else it is my loss.... You buy something in $ so you get refunded in $.... simple as that