Eberron required some changes (action points, etc) so it is out, and since they want to showcase D&D in all its glory it will have to be a higher magic setting (so psionic and low magic settings are out). Also, they'll probably want a setting less grim and gritty. They'll want a setting to glorify the game and the players, that has a lot of options and posibilities so as to match the interest of almost any player. Not to many in your list can do that, and when you take the rest of the factors into account there is really only one choice: Forgotten Realms.
Now, I'm not saying FR is the best setting. I'm just stating that it is the best representation of what D&D, under its current rule set, happens to be. It has regions and situations that allow for characters of any level to adventure, and its magic and magic item surplus allow characters of any level to have equipment equivalent to their PC ascribed character wealth (hard to do in lower magic campaigns). It also has a less grim / gritty feel, and while some may no doubt like that feel, such a feel is - in my opinion - less useful in advertising for a game. You want a game that allows the players a fun chance at glory.
Anyway, that is my take on the matter.
I see from the post Eberron, FR, and GH are the main contenders. I'm guessing the Eberron voters chose it because it won the recent contest - despite its need for rule adjustments. GH, I'm guessing, is mostly being chosen by those enamored of that setting, despite its darker feel (compared to FR) and lower magic setting (thus preventing overt use of the many magic item properties available in the current rule set). Whether we like it or not, the current rule set for D&D is high magic. I don't see GH as a possible realization of the current rule set. Although technically everything made outside of a campaign setting is 'for GH' how much of that is really true? How many warlocks, hexblades, and ninja are in GH, after all? Yet all of these are splat book creations, which technically is for the default setting. Whereas you could probably find (or place) any of these in FR with little difficulty.