There are plenty of studies about how important representation is for groups that are marginalized or disenfranchised, of course. But it's important for everyone, and not just because we should all care about how our fellow humans feel about how they are depicted. Diversity of representation matters because it creates that gameplay we mentioned - the more welcoming your tent is, the more will come stand under it. To retain and even grow a base you need to lure them in, and diversity is indeed a lure. As cynical as it may sound, having a game world which acknowledges in story the wide variety of us that exists, that plays and lives in said world, is healthy for that game not merely in a socially conscious way.
In a purely mercenary, self-seeking way, diversity costs you little and gains you much. When contrasting Blizzard with Bioware, Rob Pardo made a key error in my opinion -- he seemed to assumed Bioware was being inclusive purely because the narrative demanded it. Let me state now that I believe Bioware is wholly self-serving (and that there is nothing wrong with that) when they attempt to be more inclusive in their storytelling. Think of the narrative of your game as your recruitment poster. You need to ask yourself if you only want to recruit from pool A, or from the much larger pool B which pool A is merely a subset of, dwarfed by the larger collective? If you don't make gay players welcome, and they don't play your game, then that's them lost in terms of that gameplay you were talking about. That's their money gone, that's their voice gone on Twitter and Facebook talking up your game, that's them not buying it and that's them not playing it. The pool of players shrinks because you've artificially winnowed it down.
Now I'll say again -- I agree with focusing on fun gameplay over narrative. (This may sound strange from a dude who loves Warcraft lore.) But the focus on gameplay doesn't preclude making simple tweaks to include others at effectively no cost to you as a developer. How does one include gay characters, for example, in World of Warcraft? By including them as you would any other character, and making their being gay no more important than you would make their being straight. Your new quest giver, say, is an orc warrior - have him say that the Alliance dogs slew his mate, and later, have the players find said mate... and it's another orc male. That's right, I'm saying all that would be needed would be for us to find Mankrik's husband.
This costs practically nothing in terms of time or emphasis. The only reason not to do it is if you value the opinions of those who just can't accept a world where women can do things for themselves and/or that gay people exist. And by accepting those opinions, you value them over the opinions of those women and gay people (or any marginalized group). Further, it's a mistake to believe that including them is a political statement.
In a way, it is a political statement, but its just as much a statement not to include them. Geddy Lee knew what he was talking about when it comes to this issue. Choosing not to decide still is a choice. Mists of Pandaria actually did a much better job of this than people realize, including many prominent female pandaren in positions of importance simply as if it was of no consequence - their being women wasn't their character. They just happened to be. And that works -- it's powerful and its easy to do. Do more with it, would be my argument, because it costs you almost nothing and gains you quite a lot. That currency of respect the editorial mentioned is purchased with decisions just like this.
I don't believe this to be a decision born of malevolence, I merely believe it to be mistaken and short sighted. You don't have to be focused on storytelling first and foremost to care about these decisions, and making them with an eye towards making people feel included doesn't have to be seen as some attack of social conscience. It can be seen for what it is -- a smart decision for the future livelihood of your property. It may be cynical, but a small effort in game design can reap huge dividends in terms of enlisting a more diverse player base to not only play your game (and pay you for the privilege) but to sing its praises.