They're not necessarily talking about just those items. The entire store is designed so you buy things you weren't intending to buy. You never said/thought: "Ooh look ice cream's on sale..." and failed to resist?
Exactly, I rarely add anything from the checkout lane area, but I'm often enticed to buy unplanned stuff from the ethnic foods aisle, and now and then I'm taken in by the end-cap displays featuring product pairings, especially if I've been inclined to try a similar combination.