It really isn't as dangerous as it might appear, but it is still a waste of gas. In theory, a spark from the spark plug could blow it up, but then again so could the starter. Actually, operating any electrical switch around gas fumes (whether gas is pumping or not) has a tiny spark, and a chance of an explosion (including that cell phone).
No, the world isn't 100% safe even if we are regulated to death. But I can think of things that are more dangerous than running the engine while pumping gas. Like driving to the gas station, smoking, taking your prescriptions as directed, and eating the poison that the food companies pass on as "food".