Personally I have to applaud the fact that a business established this policy amidst the "customer is always right" consumer mentality in the US. It's far more reasonable to require people who otherwise do not take their "size" (ahem) responsibly to pay double. It's unfair to those around them to have to suffer for it.
The US is by far the most forgiving of consumers than any other country, with all the lawsuits like Mcdonalds coffee spilled on the lap and bookcases that fell on a customer because they were climbing it. It's f#@%ing ridiculous, and the people who take responsibility for their own stupidity suffer because this kind of thing has to be factored into the pricetag.