Avis - We Should Try a Little Harder

Gas is expensive, I get it. What I don't understand is what that has to do with a rental car company. In theory, they only pay for one tank of gas in the life of each car (the first one). After that, each renter has to either fill it up themselves or pay some crazy amount per gallon to the rental company. So, imagine my surprise when I noticed that Avis added an "automatic" $13.99 fuel surcharge for renters who drive "less than 75 miles". Wait, what? Now, to be fair, they did remove the fee after some bitter complaining on my part (and waving of my gas receipt at the guy) but still, if the tank comes back full, that seems a little like stealing to me (or at least double-dipping). There was some argument that it would have been cheaper for me to have taken their deal and not filled the tank. I had to bust out the advanced math skills and explain that $13.99 was in fact greater than $8.99. That ended the discussion.  Are they just hoping that people are in too big of a hurry to notice the fee?