At the scale Starbucks will single-handedly bring them to, you really think they'll be using the default pricing?
Regardless, they're very clear on the post:
>Square will process Starbucks U.S. credit and debit card transactions, which will significantly expand Square’s scale and accelerate the benefits to businesses on the Square platform, especially small businesses, while reducing Starbucks payment processing costs;
Loss leaders can be a good idea sometimes, but when you're dealing with the sort of volume that Starbucks deals with, losing any money at all per transaction is a truly terrible idea.
Regardless, they're very clear on the post:
>Square will process Starbucks U.S. credit and debit card transactions, which will significantly expand Square’s scale and accelerate the benefits to businesses on the Square platform, especially small businesses, while reducing Starbucks payment processing costs;
Starbucks saves payment processing costs. That's benefitting them.