The math works out such that there are a precise number of bitcoins in the system, ~21M IIRC.
> The amounts are infinitely divisible.
8 decimal places.
Is that alot? Yes, but my point was that the current system is leaky. The rate of leakage may not be too bad now, but as the adoption rate goes up more careless nontechnical folks will get involved. Those people will fail to backup their wallets; that BTC will evaporate is an inevitable consequence of success.
This is a client-specific value, and not a necessary property of the protocol. They can become arbitrarily divisible by simply modifying the client code.
Of course new clients will not be compatible with old clients.