The takeaway from all this is that mobile shopping only strengthens the competition for share-of-wallet.

FORBES: Smartphone Shopping And The Retail Fulfillment Blindspot

"The point is we can grow share-of-wallet as well as the number of stores, " says co-president Robb.

FORBES: Magazine Article

But in 2008, it shot up to 17-18% of spending, meaning that spiking wallet share for gasoline had to come at expense of other categories.

FORBES: What $4 Gas Would Mean for Consumer Spending