The Assembly rules. Or, more specifically, the Democratic majority in the Assembly does.

As expected, the signature component of Michael Bloomberg’s PlaNYC program, congestion pricing, was killed this week by Assembly Speaker Sheldon Silver and his Democratic caucus.

As if to underline the absolute discretion that these 107 state legislators in the Assembly exercise over major state and city legislation, the final blow to the bill was administered on April 7 in private—a committee killed it before it could even come to the floor. Mr. Silver’s members had spoken to him, they said afterward—and he listened.

The mayor, who now heads into his last year and a half in office with little time to fashion any more sweeping plans to crystallize his legacy, was predictably incensed, saying afterward that the Assembly Democrats had shown “a special type of cowardice” in not allowing members—including the Assembly’s easily forgotten, utterly powerless Republican minority—an up-or-down say on the matter.

The day after, editorial boards, too, expressed their indignation at Mr. Silver’s actions. The Times led as follows: “Rarely does one man have a chance to do so much harm to so many.”

The speaker was unrepentant.

Asked by phone on April 8 about the mayor’s criticism, Mr. Silver said, “It’s funny. If you read the newspaper accounts, the front page of The New York Times is loaded with individual members telling The Times they’re not prepared to vote on this legislation. So, it’s not a matter of one person. I mean, I, as one person, probably would have voted for the bill. But clearly the case wasn’t made, or convincingly. That’s why the bill did not succeed. When you say one person, it works both ways. He’s one person as well.”

That is undeniably true. And as the system is currently structured, what happened to the mayor’s bill isn’t anything unusual at all.

The Democrats enjoy a veto-proof super-majority in the 150-member Assembly. This means that they can pass bills without involving any Republicans. It also means that as long as he keeps his Democratic members happy, Mr. Silver can be in charge for as long as he decides to stick around.

Not only does the outside criticism of the Assembly and Albany’s fetid political culture from the likes of Mr. Bloomberg or The New York Times—or Eliot Spitzer, for that matter—not hurt Mr. Silver, it actually helps him among his members, who are wont to rally around the man who stands up for them, and for the system in which they operate.

“Here’s a guy who survives by listening to his conference,” said Democratic consultant Hank Sheinkopf. “They can vote him out in any minute. What would you rather have? A mayor that is mad at you for a year and a half, or a conference that is mad at you for a day and throws you out of office?”

The way the Democratic members see it, opening potentially contested votes up to all the members of the Assembly would be a voluntary abdication of party advantage. The will of the majority of Democrats, they point out, correctly, might not be done.

“If you had 44 Republicans and 32 Democrats, you could theoretically pass a bill that a majority of the Democratic conference opposed,” said Assemblyman Richard Brodsky of Westchester, who emerged as the vocal public leader of the opposition to congestion pricing. “That is not the way we run the system. And frankly, it’s not the way we should run the system.”

Assemblyman Jonathan Bing, a good-government type from the East Side of Manhattan, explained it by saying, “The idea that democracy did not occur here [because] it was not a floor vote really is incorrect. Democracy occurred with every member of the Assembly majority providing the speaker with his or her views, whether it was in conference or when the speaker polled members.”

Joshua Fitzpatrick, a spokesman for the Assembly Republican leader, James Tedisco, explained that whatever support existed for congestion pricing outside the autonomous Assembly Democratic conference was irrelevant. “That certainly is a numerical obstacle for us to overcome,” Mr. Fitzpatrick said. “And if you think about the support from different environmental groups, the New York League of Conservation Voters, you put in Mayor Bloomberg, our leader—it still wasn’t enough to overcome their numerical majority.”

Mr. Fitzpatrick did say his boss could use the bully pulpit, and, in fact, “Leader Tedisco issued two very strong totally public statements, one on Good Friday, one last week,” supporting congestion pricing.

Needless to say, they didn’t matter.

“The process works in ways in which the committee structure weeds out bad bills and kills them,” Mr. Brodsky explained. “In this case, the issue was so important that the conference substituted for a committee meeting. It was a committee of the whole, as it were.”

Periodically, it seems, enough people recognize the power that the little-known members of those committees wield over the affairs of New York for it to become good politics to get mad about it.

Congressman Anthony Weiner, a mayoral candidate who opposed congestion pricing and the West Side stadium—the last grand Bloomberg plan to have fallen victim to the disapproving inertia of Mr. Silver—said he thinks mayors, as a matter of course, should have more autonomy in controlling the city’s fate.

“We—as business leaders, as leaders, cultural leaders, civic leaders in the city—have to start asking this larger question of, why it is that so much of our fate as a city rests in the hands of Albany?” Mr. Weiner said last month during a speech at the Harvard Club. “[W]e in the city are functioning, we’re the adults. We should be supervising them.”

Mr. Silver, no doubt, will beg to differ.

“I have plenty of bills, you can check my bill introductory record, that have never seen the light of day here in Albany,” he said. “That’s the legislative process. We have a very diverse conference. Sixty-five members from the city of New York who represent the same people the mayor represents, and the City Council represents. That’s what happens.”