This is probably just conjecture, but, from http://www.osmond-riba.org/lis/essay_mcdonalds.htm:
Evidence showed that McDonalds served their coffee so hot to save money. This let them get away with a cheaper grade of coffee and cut down on the number of free refills they had to give away. McDonalds executives testified that they thought it would be cheaper to pay claims and worker's compensation benefits to people burned by their coffee versus making any of these changes.
_________________________
Bitt Faulk