OK, that makes more sense. If the individual Bitcoin is divisible to 9 decimal places then I can see it has the potential to handle growth too.
21,000,000 is arbitary .. it makes more sense.
At the end of the its all about the 'perceived' value by the masses. That is what drives every market = supply and demand of course, but also - the madness of crowds and crowd psychology.
This can lead to runs on banks or overinflated housing prices .. and often both at the same time.! :-)