An online merchant cannot afford to directly take credit cards until he is doing a couple of thousand dollars per month. Until then it's Paypal, which is about a 6% transaction fee, and scarily unreliable.

So a 5% discount for Bitcoin is a win. A few cents more cash, and a lot less pain in the anatomy.  For the immediate future, neither conversion cost nor inflation are relevant: There are already a few monthly expenses, hosting was the first, that I can pay in Bitcoin.

Until you have been an extremely small (like, supporting one family, small) retail merchant, you have no idea how horrid credit cards and Paypal are, and thus how much it is worth to avoid them.