Why am I getting different numbers of search results on google.com in China?

No it's not a rhetorical question. Google has openly admitted to censoring the search results you get when you search on google.cn, but it never said and I think in fact would deny that it censors google.com searches. Yet recently I was doing a very innocuous search, looking to see if "of CEO" or "of the CEO" was more commonly used. I typed both in quotes in google, and was surprised to see that "of CEO" got more hits than "of the CEO", which sounds way more correct to me. Later, I did the search at work, where we have a VPN based on a US server. This time, I got more hits for "of the CEO" than "of CEO"!

Finally I searched again at home and got the same results as before, so I turned on Tor and tried again, this time getting even more results than I got when I did the search at work! Photo evidence follows, starting with a pic of the search done without Tor, and then the one done with Tor: