I don't know what the actual situation is (I suspect that nobody outside of Blizzard marketing does), but I feel obliged to point out a scenario which is admittedly contrived but which I believe to be reasonable, in which Blizzard isn't marginalizing women and has still only released videos with men in them so far:

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Blizzard invites fifty celebrities to record videos advertising that they play World of Warcraft. Half of the invitations go to men, half to women. Of the invitees, forty refuse; of the ten left, seven are men and three are women. All of them agree to record ads as their schedules permit. The first in the studios are Mr. T, Verne Troyer, William Shatner, Willy Toledo, and Jean Claude van Damme, and these videos are released as they are recorded. (Troyer's is delayed for unspecified reasons.) All five are male.

At this point, therefore, Blizzard has positive responses from three women and seven men, despite sending queries to twenty-five women and twenty-five men. None of the women have recorded; five of the men have. And the five (well, four, Troyer's is delayed) men's ads are the ones that have run.

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I don't mean to say that this is how it happened, and I don't mean to say that Blizzard isn't marginalizing women. I'm just saying that four videos (and a fifth that hasn't aired yet) isn't really a whole lot of evidence on which to base the assumption that they /are/.