It has been my experience that the DM typically has final say in all matters related to the game, the genre, the house rules, etc. A good DM typically respects the opinions of the Players, but when push comes to shove, the DM has the final say. (If another person is hosting the game, then that person has final say on all matters related to the use of his property, but that wasn't covered in the poll above.)
A lot has been said in other discussions about every Player having their own form of final say, in that they can vote by not playing in the game and finding a better use for their time. Everyone has that right, and that's the reason why good DMs respect the opinions of their Players.
However, the DM has that right, too, and without him, there is no game. Therefore, by default, he has final say.
I tend to game with groups that are not so insular that they only game with each other. I game with several DMs, each of whom have their own gaming groups, which I may or may not be a part of. That's how it has to be viewed, in my opinion, in this kind of environment. Were I living in a place where the only gamers were the five other guys sitting around the table with me, then yeah, I could see having to deal with the kind of issues related to gaming by committee, because there is simply no other game in town. Social dynamics should create appropriate boundaries. (They don't always do so, but the wise and smart DM is the one that pays attention to such.)
However, I am fortunate in that I live in a place where tehre's more than one game in town, as do many of the gamers that actively play RPGs. Even if I didn't, I have access to the internet, and there are online tools that allow me to game "face-to-face" using electronic tabletops, so I don't think my position would really change, even if there were no other game in my immediate area.
I often wonder about the bad gaming experiences of those who feel forcefully that the GM is not the final arbiter in matters related to the game, because there's only one reason I can think of why someone would have problems in this arena: they've ran into a bad DM or similar authority figure in the past (likely a control freak with limited social skills or experience), and they've been hurt in the process. If you are trapped in such a situation, I would suggest that you do yourself a favor, and get out. Find another group. It's not worth trying to control a bad DM, because then you're playing their head games, and you've already lost.
My Two Coppers,
Flynn