Ask the Readers 1: Tiananmen Closed at Night?

I seem to be developing a bit of a readership, for the life of me I've yet to figure out why, but I deeply appreciate all those who come here and sometimes even find it necessary to comment on my crazy ramblings. That said, I want to especially thank zhwj for enlightening me about the "Chinese pizza" phenomenon, for those interested in trying them, I guess there still are a few stands alive and kicking at Xidan. I also want to thank Laura for her interesting story. I'm forced to do this in a post instead of in the comments section because I'm fighting the losing fight, still using blogspot, which is still blocked in the PRC.

Here goes part 1 in Ask the Readers, a new (ir)regular post where, when I don't know something about China and am willing to admit it, I turn to you, my dear readers for help and hope someone answers the call.

Despite living a stone's throw from Tiananmen Square, I've rarely ventured there over the past few months. On the two occasions that I have (both in the evening), I've been surprised to find the Square totally empty. The first time I thought it just might be too cold (but still, absolutely NO people?) or that there must be some kind of gathering that I hadn't heard about, but to have come across this situation again doesn't seem like a random occurrence.

So does anybody know about this? Has the government taken to closing down the Square to the public after dark as a potential Olympics protest or gathering spot precaution? Is this only for a winter cleanup in preparation for the Olympics? Is it just coincidence that I happened upon the Square the two times there have been large, unannounced events in the Great Hall?

Any answers to this (or other wild hypotheses) would be greatly appreciated.