Haagen-Daz (and Baskin Robbins) ice creams are expensive in China because they are actually imported, not produced in China under license as are Nestle and some other products. Also, the Chinese gov't taxes the heck out of imported foodstuffs (WTO, where is thy sting?). And then at the airport, you have the captive markup.

I do agree with eating beforehand, afterwards, or taking your own onboard snack. I usually wave off the Chinese domestic in-flight meal.