I usually think the "candidate doesn't know the price of a gallon of milk" type of stories are pretty stupid.
But the price of gas, today, is a different issue. Unlike milk and similar, the price of gas is pretty much a staple of the news these days. Glance at a newspaper or flip on teevee news (local, cable, network, whatever), and you'll get the daily update of the price. This isn't just about a presidential candidate who obviously and understandably doesn't fill up his gas tank very often, it's about a presidential candidate who just isn't paying any attention to what's going on in the world.