But, what do I know, I'm still stuck on trying to explain
the difference between a client and a protocol to people (just as I did back in the MSNChat/IRCX days).
This is an extremely important observation. The difficulty resides in the fact that if there is a de facto software monopolist, his software (his client) is at the same time the protocol definition. What we are observing, is that this monopolist is losing its ability to dictate the protocol and its changes. The protocol being confused with the software written by one entity, and hence, entirely centralized, is becoming detached from it, and hence, is slowly gaining some form of decentralisation. Not quite yet, because for the moment, there seems to still be only one *trusted* piece of software out there, but the deciders in bitcoin (the mining pools) seem to have decided not to follow blindly the implicit protocol changes any more that the software monopolist is shoving them up with.
I like to compare bitcoin to a parliamentary monarchy, where the King is the only entity able to propose and modify laws (the software monopolist is the only one able to propose modifications to the protocol, by including it in a new version of the software) and the parliament (the mining pools) can vote over it (by adopting them or not: that is: by signalling for it, if the King has foreseen this, or by upgrading/not upgrading if the King didn't leave an option in the new version).
Decentralized, not at all. You can hardly think of something more centralized than this. That said, it worked well, because the King was "good". Nothing works better than a monarchy where the King is an enlightened being with good intentions.
The troubles we are seeing, is that this entirely centralized monarchy is losing its grip and decentralisation is slowly gaining field, and the King doesn't know any more how to restore his absolute power.
If the system is truly decentralized, the protocol should become entirely immutable.