Procrustean Coke

There's a donut shop on the corner that I walk by often.  It has a sign on the window that's piqued my interest:  "Coke, 89 cents, any size"

In a way, I like this.  Instead of one size fits all, why not one price? But isn't it odd?

First, how likely is it that people will get anything but the biggest size?  Even if you can't finish it all, you can save it for a while, or give it to someone else, or toss it when you're finished.  But if you get a smaller size, and there's not enough, you'll curse yourself for not taking advantage of the deal.

And is the biggest size meant to sell for 89 cents, and everythng else a ripoff?  Or is the average price 89 cents and they're taking a chance. Or is it a loss leader? (Though who buys coke with a donut?)