As anyone who's spent much time in American supermarkets will be aware, this kind of supersizing is hardly unusual. It seems to have evolved in response to two common features of American grocery shopping: people drive to the stores and they have the kitchen real estate to store things. And it has its advantages: if you do go through a consumable quickly, then buying the big jar gives you a better value per ounce and less packaging waste.
However, the sheer amount of American food waste--perhaps a quarter or a third of the country's consumable food --suggests the illogic of this approach. After more than a century of shrinking, the size of the average American household is growing again, partly because people are consolidating due to the recession. Still, it's very few of us who live with a clutch of hungry farmhands. And regardless of how big our cars or our refrigerators are, most of us go to the grocery store routinely to buy perishable products like fruit and vegetables. Some decisions are based on cost per unit, but others aren't and shouldn't be. If you only need a few units of a product it's better (and, often, less expensive) to buy what you need than to get the big jar and bin most of it, which is certainly what will happen to this mayonnaise.
I think there is a market for "right-sized" groceries, for this and other reasons--notably health, which is why we've seen a lot of companies come out with portion-controlled servings (100-calorie snacks, 8-ounce sodas). Interestingly, some companies are also downsizing for their own reasons, on the premise that if you reduce the content but not the packaging they can save money on supplies while still charging the same amount for the product. I'd rather they shrink the packaging too. Some customers will care--the woman cited in the New York Times story at the link has nine children--but some won't notice, and some might even prefer it.