For all intents and purposes, Shiggy, Kojima, Spector, Wright, amd Molyneux are more or less responsible for the games their names are on. These are guys with enough authority within their organizations to go as far as to say "Fuck this shit, start it all over" and have the team actually comply.
Which is not to say everyone who has their name attached to a game necessarily deserves it. Yuji Naka for example is not the creator of Sonic the Hedgehog; he certainly deserves mad credit for the really sophisticated programming in that game (it's way more complicated than it looks on a machine that's way more underpowered than was advertised) but he did not come up with the idea or produce the game. He is probably responsible for Nights and PSO though, so suck on that.
But I think overall if, say, American McGee sobered up and decided he wanted to actually make something of his own, he'd get socked in the face every time he tried to push an actual decision.