Every gas station picks their own hold amount. Clearly this station which is part of Stop & Shop finds that Discover users fill up a lot and have a higher chance of bouncing. You have to remember that holds are there to guarentee that funds are there and since credit card users usually don't care since they only get charged the correct amount in the end making the limit high only messes with debit card users and those with low ceilings. That is why for debit cards they usually set it at $50 as a convenience. The pumps are actually connected quite well most of the time so they can update the charge as soon as you finish pumping or within 15min.
