So in other words the client with the largest install base ultimately makes the rules. The fact that source code is available is utterly irrelevant to the vast majority of users as they would not have the expertise to derive anything from it. So rather than having monetary policy dictated by the Fed, Bitcoin users may ultimately have it dictated by those responsible for the dominant client application.
You're looking at it backwards. I'm beginning to think this is habitual with you. Bitcoin users decide (by using it) the dominant client application. If the one they're using implements rules they don't like, hey presto, they change clients, and it's not dominant any more.