Yes, exactly (and I don't believe the article implied what you said.) People with low incomes make rational spending choices. By offering a financial incentive

Yes, exactly (and I don't believe the article implied what you said.) People with low incomes make rational spending choices. By offering a financial incentive to use the vault, Wal-Mart is trying to make saving as attractive as another possible purchase. Borrowing your language, saving becomes a difficult choice instead of an easy choice not to save.