After having a look around, ChinaJoy is an Expo for digitally related media. There is a lot of video and online game booths and I found a few of the larger presentation areas had cosplayers dressed up as characters from the game participating in the marketing effort. I haven't been to game events in other countries but I wonder if the same thing can be found at similar events. Here are some pictures of cosplayer I found around the 3 large convention halls.

I like the second picture, you can see the boredom on the faces of the cosplayers. Of course they have been cosplaying for hours now, this kind of work is not like a short 3 or 5 minute show.