Come on we are comparing chickens with debit cards now? You might make enough to consider 50 dollars a little cash but I am not in the same boat as you. In all my years of going out for food and beers I have come across two places that didn't take debit and they have both been in the past month.
I would assume that it does have to do with the charges incurred. For a retailer to have a credit/debit machine they have to pay a percentage of the sales to VISA/MC or your bank. Credit cards are a gimme as the majority of our society runs in the red when it comes to finances. If the pub is smaller and slower then it makes perfect 'cents' for them to take the income that an independant cash machine owner will pay them as opposed to paying 4% to the bank to authorize through the machine.
You might make enough to consider 50 dollars a little cash but I am not in the same boat as you.
Think of it from the small pub owners perspective. They have tons of costs in running their establishment. That 4% they make as opposed to having to pay may be the only reason they are there for you to enjoy. That's my thought on it anyway.