I believe the general consensus is that if they served the coffee cooler, by the time take-out customers got around to drinking it, it would be cold. Erring on the side of too hot maximizes customer satisfaction because the number of customers who would be upset at cold coffee is greater than the number of customers, buying coffee at McDonalds, who have sophisticated coffee tastes.

Anyway, Starbucks also serves their coffee about as hot as McDonalds. Turns out, coffee hot enough to cause horrific injury is rather common.