It works all the time when ignoring the times it didn't.
If a manufacturer says their manual transmission car gets 45 miles to the gallon, and Fuelly says that same car gets 39 mpg (averaged over a million user mileage submissions), is it intellectually dishonest to use 39 as the working figure when budgeting for gas?
What you interpret as a troll answer, I interpret as a reasonably clear explanation of why he chose the figure he did.