only one single "reference implementation", by a single team. That is total centralisation in my book.
Bitcoin is developed by dozens and dozens of people (something like over 400 total contributors to the Core project overall). It is a bit open source collaboration of many independent parties. Not a single team.
They are obviously not independent, and competing, right ? You can say that there are dozens of colluding entities, not antagonist competing entities, what decentralization is about. OPEC can also say that they have dozens and dozens of different oil wells. Does that mean they are not a cartel and are a competing open market ?
Bitcoin's creator was vigorously opposed to multiple implementations for sound technical reasons,
https://bitcointalksearch.org/topic/m.1611Satoshi understood the dynamics, and so do most competent potential contributors-- which is why they choose to collaborate with the Bitcoin project rather than go off and create something that will almost certainly be incompatible.
This is also why I said that he made a fundamental mistake, and,
no, Satoshi didn't understand, or if he did, he took an opposite public position, to what decentralization and immutability resulting from antagonist consensus, was about. He didn't realize, or fooled other people in thinking he didn't realize, that "consensus" in matters of money is of a totally different nature than consensus in any other collaborative open source community system.
The reason is that contrary to any community system, a monetary system is about antagonism of all entities, not about collaboration. A monetary system is about wanting to cheat the system and not being able to, wanting to scam the counter party and not being able to. Indeed, in a monetary system, we all want to
have a lot of money, and all want others to
want a lot of money, and a monetary system is such that we are *forced* to diminish our own holdings if we want to pay someone, even though we don't really want to. It is the fundamental desire to be able to create money at will, but not to want others to create money at will. Money is fundamentally an antagonist game.
That is totally different with, say, the development of an e-mail system, or web page browsing software, where there's no antagonism at the basis. Me wanting to send e-mail to you, has no necessity of antagonism, and we can perfectly collaborate over that.
But in monetary affairs, if I pay you, I have lost my holdings, and you have them now, and if I had my say, I would like to be able to spend them again, and if you had your say, you would like to have obtained my holdings without having to deliver goods and/or services for it, but both of us are FORCED to act this way, because the monetary system is such that we cannot get it our way.
As such, a monetary system
has to be fundamentally immutable for its subscribers, because anyone that can modify its functioning, or its history (both are intimately related) can (and most probably will) bend the rules in his material advantage.
As to why both the rules (the protocol) as the data (history) have to be immutable is obvious: the data only give rights and limits through the rules, and these enforced rights and limits is what the monetary system is all about.
And now, Satoshi invented, but publicly seemed not to realize, the immutability mechanism of decentralization:
sufficient non-colluding antagonists that are not able to agree over anything else, than the existing consensus (including the rules). In other words, all players/antagonists in the system would like to bend the rules and history into THEIR advantage, and NOT to the advantage of their adversaries (the other members of the system), so as to get a maximum of material advantage out of it. But as such, if they are sufficiently diverse and disagreeing, they cannot settle over any change, and as such, immutability results, as it is the only thing they, de facto, agree over, because they did so when joining.
A single team providing the software, however, is of course way too powerful, and much too colluding amongst their community members, for this mechanism to work, but there is now, finally, some counter action from other members/antagonists in the eco system, to turn bitcoin in a truly immutable system (protocol included of course).
Satoshi's public stance on "modifying the protocol later" make me think that 1) he didn't get a clue about immutability dynamics or 2) he did, and was being extremely deceptive about it.
There's a fundamental difference between the immutability of the protocol and history on one hand, and the software implementations of that protocol on the other hand.