There's a very small amount of people sitting on a great deal of coins. If there were that many people clamouring in quick succession it's quite possible sellers would just go on strike and the price would way overshoot a realistic value.
IMHO those very few people actually control the majority of bitcoins. This is a problem that not many people like to face or address. It is one of the things that keeps us from hitting mainstream.
Top Hoarder: "Hey world, accept this new form of currency. Sure I own and control 8% of all of it, but it is great. DECENTRALIZATION FTW."
World: "No thanks, that would give you singly way too much power. I think we will find a different way to revolutionize money."