[Elepsis]

It seems like you're suggesting that people are buying the small cans of Coke based on endorsements like this one, and then chugging three cans in one go to make up for the super-sized drink they'd otherwise have gotten.

What exactly is that assumption based on?

It's been abundantly demonstrated that smaller servings do help people follow through on efforts to reduce their food intake. I don't see any reason Coke should be different.