UPDATE: Kurt Groetsch sez: "Two more photos of salad bowl extensions here and here. They made the rounds of the office when I was working in Beijing."
Gregory Lam sez: I have a friend of mine who currently lives and works in China, described the same phenomenon here. "I quote: 'For one price (I think it's approximately 20 RMB), you get a single trip to the salad bar. You get a medium-sized soup bowl to put your salad in. Of course, this is a challenge any structural engineer would love to take upon: putting the most salad you can in this small bowl. I saw people at the salad bar for 5-7 minutes just trying to force more and more salad into their bowl. The highest salad I saw must have rose 9 inches off the top of the bowl.'
"The reason is, Western food is quite expensive in China. Pizza Hut is actually considered to be upscale dining!"