HDFC Fuel Surcharge Reversal

One thing I have recently noticed regarding refunding of fuel surcharges, the extra amount that is taken from you when you pay for petrol/diesel at fuel pumps using your debit/credit card is this:

If you pay for it via HDFC credit card, then it takes away some amount, say x rupees. But after few days when the bank refunds you the amount it won’t be whole of that x rupees. The bank keeps a small amount from that for itself.

But when you pay using a HDFC debit card, the amount that you are charged is completely refunded back to you, to the very last paisa!

Now I don’t know the reasoning behind this, but this is correct atleast for the EasyShop Business Debit Card (MasterCard) that I got.