retail news in context, analysis with attitude

The Wall Street Journal has a story about why falling gas prices are good for Costco, offering two reasons...

First, the story says, "For most fuel retailers, falling gasoline prices mean revenue suffers and margins rise. The result: Profits don’t change all that much. A high-volume seller such as Costco, though, captures falling wholesale prices at a faster rate than smaller gas stations. At the same time, it can be slower to ratchet down its retail price than nearby gas stations. Costco pockets the difference, boosting profits."

Second, "Consumers are more likely to schlep to a distant warehouse store for even lower prices, and then have more cash to spend on nonfuel items when they get there. And they may return more often than otherwise would be the case to keep filling up the tank."
KC's View:
I must confess to being a little confused by the assertion that Costco actually gets a little bit more margin when gas prices drop ... because I thought it was an article of faith at Costco that margins could not go above a certain level and that all savings had to be passed along to the shopper. Is it possible that gas is an exception? Or that certain articles of faith are not as inviolate as they used to be?