Braintree's core product is a payment processing gateway. If we go down, get hacked, or introduce serious bugs, our customers can't run their businesses. As I said in the article, we pair for almost everything, and we find it helps us write great software that stays up and stays secure.
I should have focused on the distinction between the size of companies -- that seems like a more accurate framework. I suppose I meant "performance" in the sense of low-level algorithm efficiency rather than high-level scalability and reliability. A misuse of the term on my part.