10k-ish is about as low as I've seen in maybe forever by my recollection of things.
Bitstamp had 10k asks as well not long ago. Far from that now. When the price goes up, it is normally because the asks are being bought so there are less left to buy. I assumed most people knew this.. 21k BTC left in asks on MtGox now. Total.
It is probably as or more accurate to say that as the asks disappear because they are gobbled up, the price goes goes up. Just sayin'.
I dunno where you are seeing the 21k asks on Mt. Gox. As I type this, that figure seems like a decent estimate for all visibly available BTC on all the exchanges combine. At least for anything roughly within 100% of current spot.
If I was a betting man, I'd bet that some of the larger pac-man types are taking advantage of the fact that most normal humans are soundly asleep and thus not in a state of consciousness required to pull their asks before it's to late.