I think mirelo's argumentis absolutely right - bitcoins will be lost; people die and don't pass on their wallets, move on to other monetary systems, etc. If I walk away now, .018ish bitcoins will be lost from the system forever. Laugh now, but if 20 years from now that is the equivalent of $100000, not so funny.

A lot of people on these forums like to dismiss arguments like these because they are "so far in the future that it will never impact us" rather than evaluating them for the long-term viability of Bitcoin. It's somewhat disappointing, especially when at some point in the future, it will become a real problem. Having a billion people trying to trade in Bitcoin at 8 decimal places .000000010 won't work.