There is how many have been mined, and are an upper bound of that many bitcoin in circulation. Some of it is stuck with forgotten addresses and passwords, so some are just gone- I think bitcoin won't be used by the time we have enough computing power to track down dead addresses and crack the passwords.

Also, the short term price sensitivity of bitcoin is related to the depth of the order book and not the total market cap of coins. Someone placing a sell order at market rates for 94k bitcoin would wipe out the order books and the price would go way down, and take quite a while to recover. To sell 94k bitcoin without nuking the price they will have to sell at a slow trickle.