Almost two decades ago, I worked at a network service provider who had as a customer a company that provided the technology for serving those gas pump ads.
At each gas station they had a VSAT, a router and of course the digital signage boxes on each pump.
They fed the ads to thousands of pumps via a single T1 to HughesNet in Atlanta. They'd multicast the ads, and have a local cache at each pump that would receive the stream, cache it and serve it.
It was one of the most elegant setups I've ever seen, and should serve as a case study in multicast for efficient bandwidth utilization across an expensive data transmission medium.
Unfortunately gas stations don't actually make much money from selling you fuel. Most of the money is made from the attached convenience stores.