Credit Cards Cost

Here is an article from Michelle Singletary who is a syndicated columnist whose columns are in the N&O frequently. Here is an interesting quote from it:

Peter Tufano, a professor of financial management at Harvard Business School, has found in his research that transaction credit card users -- those who pay their bills off every month and who are not overly indebted -- are more financially literate.

"Their credit card purchases are under control," Tufano said. "But that is not to say that they are spending less."

Greg Davies at Britain's Warwick University found in one study aimed at marketers that customers using credit cards spend more than those paying with cash or checks in purchasing situations that are otherwise identical in every other respect.

In the end, I understand this is generally true. But, if we would use the credit card for just something like gas and no other purchases, is that still true? I still can't buy it being true in that limited use scenario.