Bitcoin is decentralized.
no it is not. Asic farms has made that thought process wrong for quite some time.
The only coins that are truly decentralized are the ones that require GPU mining only; for the time being.
Give it time (profitability) and someone will be running a farm of thousands of those as well.
oh and on the subject of 21 million coin supply, that is wrong as well because people have lost their coins, satoshi's have never left his/her wallet so there will be less than 21 million always. Unless someone crafts code and forks bitcoin to regenerate those coins, it's impossible to have 21 million coins in the supply chain.