I see your point, however, the my focus has a 13 gallon tank, so even a $0.02 per gallon price difference will only equal a $0.26 difference in cost for a full tank of fuel, and unless you drive by many gas stations daily (I don't), driving out of your way to save $0.26 is a little silly. For me, with my gas consumption, I would be lucky to save $2.00 a month by price comparing different stations, and that is assuming I don't use any more fuel by driving out of my way to get to the lower prices.
For someone who fills up daily or has a vehicle that uses more gas and has a larger tanks, and fills up more often, it might have a small impact on gasoline spending, but nothing significant.