Penny wise, pound foolish!

[tbn.al]

One of my friends let me in on a secret after last night's orchestra rehearsal. I mentioned I had to stop for gas on the way home and he told me where he goes to get cheap gas, 10 cents under the average local price. Trouble is....it is 10 miles out of my way, and his too, to frequent this particular Kroger store. His car gets 20 mpg and has a 20 gallon tank. I quickly did the math and told him it cost more to drive to the station than he would save. 20 mi = one gallon of gas at 2.40 to save .10 per gallon on 20 gallons = neg .40. He nodded in agreement as we both cranked up to go home. When we got to the fork in the road I turned towards our houses and he continued on towards the distant Kroger. What am I missing here? Oh well, he's a french horn player.