That is pretty annoying. I can understand if you stop and get gas, and no one else is at the pumps, leaving at the pump to go inside. Sometimes the place might get have a surge in traffic and suddenly... your car is blocking the pump. It happens. But IMO most of the time it's just flat out "and I care because...?" attitude of pump blockers.
Although, I bet the gas station would prefer you to leave the vehicle parked at the pump. I don't know what the statistic is, but I bet most people who go into the store do so to pay (maybe they get other stuff too but I bet most pump blockers are going into to pay cash). So, if you gas and then go to park, they need to monitor you specifically to make sure you're not a drive-off. All the people who get ticked off at pump blockers are probably the ones who never go inside.
OT: when I had my diesel car I would want to use the D2 pumps out front, as the truck pumps require prepay. Guess what two pumps would always be blocked... and every other gas-only pump would be free. Grr...