A less expensive payment network is one reason bitcoins might be used. Ask ten people why they use bitcoins and you'll get ten different answers. For some, it will be the ability to send money without needing a bank. For another person the reason might be related to the anonymity that bitcoin offers. Bitcoin's benefits range from supporting micropayments to supporting large transfers with no chargeback risk.

But for the long term, When the list of payment methods reads:

  Visa / MC / AmEx / Bitcoin (receive 2% discount)

which button do you think most consumers will choose?