I haven't done the math, but I don't know how accurate this is given that 2/3 of their sales are to members who receive 2% cash back ($110 executive members). The executive membership would need to average $5500 in purchases to wipe out any Costco profit on their memberships. $8250 average to wipe out ALL membership profit.

I'll have to come up with a formula based on the numbers in your article. It'll be interesting to see how accurate that "profit from memberships" statement really is.