Speculation at places like Goldman Sachs isn't just about having better future-predicting power, though. It's also about sitting on buckets of money such that you have a lot of risk tolerance. Then people pay you to take their risk, and you win on the average (in terms of profit) and they also win on the average (in terms of reduced risk).

Starbucks, being as big as they are, may simply have felt that they were big and well-informed enough that the risk of self-insurance made more sense for them... a decision which is easy enough to snipe at ex post facto, but may still have made more sense.