Anybody with $700 can start mining for a current cost of $2 per bitcoin and sell it for 13 times the cost.
So yeah it's a bubble.
If you could setup a gold mine today and mine gold for $115 an oz and sell it for $1500 oz how long do you think gold would continue selling for $1500 oz.
But bitcoins are not infinit, as gold.
As far as we know...
It's simple the ease of entering the market means more miners are coming.
I'm sure there's a endless supply of people in the world who would be happy to make 30% on their money mining bitcoins. Which means say goodbye to 15 times your cost of productionin the near future. It doesn't matter about the end supply number of bitcoins. Competitive mining is coming which will lower the price of bitcoins.
The Mining forum is full of people saying mining isn't worth it. They're only saying that to discourage people to mine(they want it to themselves) by saying that it encourages people to buy bitcoins which miners are selling to cover their costs.