Heh, I made a comment to that effect years ago and got absolutely dog piled for it. Pages and pages of people telling me what a terribly entitled player I was to even suggest that the DM doesn't have the absolute right to ban anything at the table for any reason.

Times maybe have changed a bit.
Yes, it seems I'm in this minority as well.
I'm finding the whole conversation fascinating. I understand DMs wanting to ban things because they genuinely believe that it is mechanically broken. Very few of the comments in this thread of of that class, however. The majority (self-selected, admittedly) do like to ban their players playing things, because of the personal taste of the DM ("I don't like/hate x").
This is completely foreign to my experience as a player, and consequently as a DM as well. Even if the dwarves have all been hunted and killed in the setting, if a player wants to play a dwarf, I want to work with him to make that happen (and I recognize that by saying that about dwarves up front, I am actually encouraging players to want this). Even if there are no orcs in the setting at all, I can find a way to get the mechanics of the half-orc into the setting without any real difficulty -- reskinning is trivial if the player wants to make it happen too.
I can understand not allowing non-core* options for various reasons (power-creep; the belief that it's underplaytested or disruptive; or due to accessibility -- i.e. mechanical or practical reasons), but if a player wants to commit to a certain story knowing the default assumptions of the setting, I don't see why my like/dislike of that particular race or class should even become relevant. As a DM, I've already get to control the entire universe at the table -- the player just gets one character.
I think I count myself very lucky that I've never had one of my ideas "banned" because the DM doesn't like something. Judging from this thread, I'm in a rare minority.
* I do recognize that the distinction of core/non-core may come to mean something very different in the new edition. With all the options the DMG will apparently offer, there will be some that are in, and some not. My instinct, though, is that all of the PHB will be in for games I run (incl. feats and other "optional" elements) -- even if I myself do not happen to like it.
I want my players to tell the stories that get them excited!