If you look at the numbers on that page, it is true that Han Chinese dominate the ethnic mix... 91% are Han.
What gives a clue as to homogeneous the population is can be found on this page:
http://en.wikipedia.org/wiki/Han_Chinese_subgroups
Particularly splitting up the dialects of the main group (Mandarin) and you really start to see how different each area of China is.
Cultural differences between each region are quite large as well. If we have a diverse population out of 320 million here in the U.S., you can only imagine how diverse a country like China is.
Mao's Cultural Revolution was an attempt to homogenize the population and perhaps it can be said that the Communists succeeded to a great degree. However, its difficult to erase 5,000 years of culture in one or two generations.
India is another subject altogether and another 5,000 years of history behind what makes India tick.