US Chinese food vs Real Chinese food

I've hear people that were born in China and come to the US to try our Chinese restaurants say that they're very different compared to the food that's actually served in China. 

Can someone explain the differences in our perception of Chinese food and what's actually over there?

>>17
What if it's a mixed crowd, with both Asians and non-Asians?  (no, I don't walk up to them and say, "So, what kind of Orientals are y'all?" so I don't know whether they're Chinese or not)

There's a Chinese buffet place near me that has some decent food.  The labels and menus are in both Chinese and English, and the restaurant seems to be staffed almost entirely by Chinese (or at least Asians), but the people you see eating there are a very diverse bunch of people.

If you're wondering, I am just a big, dopey-lookin' white guy who likes their Mongolian beef, especially with some chili paste on top, and their broccoli-and-chicken.