-- I can't speak to the economic implications of limiting # of bitcoins to only 21 million -- it's probably based on the fixed rate of coin generation and the desire to have it stop by 2016. ---
Bitcoins are generated until 2140.
--- Also, if you are serious about making a currency for the whole internet, 21 million seems like a few order of magnitude too small due to number of participants. --
Each coin is made up of 100,000,000 atomic units, so using the bitcoin denomination is arbitrary, and smaller denominations can be used as the value of a bitcoin increases.