"it is trivial to create another digital coinage with a slightly different protocol that behaves exactly the same way as far as a user is concerned."
The sad thing is, this will almost single handedly end the bitcoin craze. With hundreds/thousands of competing crypto-systems of exchange who in the world is going to maintain and trust in these systems? Do you see valuation agencies looking at these things and go, uh yeah this is a good valuation? They will laugh at it and say there is no valuation to judge on it. That alone will prevent most institutional investors from even toughing them, meaning realistically, the only people touching crypto-currencies are cowboy investors or people who actually want it to make exchanges. But in a system with 100's of competing products, who wants to run their business by having hundreds or thousands of highly volatile currencies as a exchange?