Its a contentious issue for some. But many institutions charge a fee to pay a bill. You walk into a store and buy a pair of jeans clearly on sale for $70 and then at the register if you decide not to pay cash you will have 1% added to the total. Its not unusual is all. Optus will apply the 1% surcharge for various billing methods. They do provide a free payment method option - direct debit.
I agree keeping an eye on the monthly bill for any contract situation that is open to variation (especially Telcos) is a must. I'm on direct debit and get an email of the bill a week or two ahead of when its due.