I have to say, in light of the facts, that the verdict was fair. If McDonalds was unaware of previous injuries, it would not have been reasonable. But, McDonalds knew from it's customers that the potential for serious burns were there.
Bottom line, while the buyer is responsible for the use of the product, if the vendor contributes substantially by creating an well known hazzard (drive through window, easily spilled cup, substance in a dangerously hot condition), they are contributing to the injury potential.
An analogy would be a gas station with pumps that filled your car twice as fast, but occassionally sparked while doing so. The benefit to the consumer and/or the vendor is not worth the hazzard, and it's irresponsible to offer it.
Now, we could talk about the lady who was paralyzed in an Explorer rollover accident; she got a $103 million judgement against Ford. THAT was ridiculous.