But does that serve any real purpose? If difficulty increases by 100x because of all the new miners does that help bitcoins as a unit of exchange? All that equipment is basically wasting power to do arbitrary calculations that only have value because of an artificial currency.
Consider this: If mining becomes insanely difficult and a newbie is looking for a way to acquire bitcoins, he/she will purchase the coins instead of mine for them. So, we'll be seeing a lot more people buying bitcoins instead of mining equipment. This will cause an increase in bitcoin value.
Also, all the mining power is going into verifying the block chain, which prevents hacking.