The difference is that the global value of gold is about 8.2 trillion and the global value of all bitcoins is only .7 billion. Also, gold is not very liquid. At least, not in as much as you can't use a gram of gold to go buy something.

With only so many bitcoins that could ever be in circulation, if they became an accepted measure of currency the global value of bitcoins could easily jump up to 50-100 billion. On the other hand, if nobody were to accept them their value could quickly drop.

This will be fun to watch.