Visa would also be a middleman. Or even the post office if you only accepted mailed cash.
And tell me, how does one cut out the middleman when they convert their Bitcoin earnings to US dollars or whatever currency they prefer?
The point of donating money to the author of the piece is to encourage them to continue writing this epic story. Giving them Bitcoin is akin to leaving a tip to your server where the tip appears to be currency but rather instead is a Chick tract with the suggestion that you'll pray for their soul.
I'm not in the mood to register with some service and hand out my CC data to give the author a buck. In contrast I'd scan a QR code in a heartbeat.