These things above fail to take in the culture aspect. Generally, "being present" is considered "work", so the idea is to be present in the office for all of these hours.
When "we" (Americans) showed up at 8a-9a, busted out an enormous of amount of code, email, meetings, etc then left at 4p-5p was quite a shock to our native compadres. One of the managers actually asked us to slow down as they weren't able to keep up and were causing problems.
A snooty person would claim "oh look how much better the American system is", but it's much more complex than that. First, the Chinese have a very interesting total life integration. You still get married at late biblical ages (15-19), your parents move in with you and take care of the kids, you generally don't own many things (including a house), and your job and coworkers are friends and very much part of your life; you'll eat three meals a day with them and talk long walks. Your job pace is much slower and therefore, hours much longer.
Americans tend to live these absurd double identities, where we have coworkers our spouses will never meet, and we rarely interact with said coworkers outside of work, which is quite a culture shock to the Chinese. There was just another thread on HN about "fundatory activities", and how badly they can go over, which simply wouldn't exist in China.
In the end, just a different system, based on completely different national ideals. It's hard to understand until you're there living and breathing it.