No, actually the probability a general or admiral would happen to be a woman IRL matters significantly because when you go through the game and insert a given characteristic such as "female" throughout the game for the sake of filling diversity or affirmative action quotas in numbers that are much greater than what tends to be observed in reality -- it causes the majority of players who realize how rare it is in the real world to have so many female generals/admirals to come to the realization they were put there for political "diversity" or affirmative action purposes. When this is done repeatedly throughout the game, it detracts from the sense of immersion and realism the game has to offer its players.
Some will argue that many things in the Mass Effect universe are not perfectly realistic. And it's true, sometimes the physics of the universe may not always be perfectly realistic... but there's a difference between sacrificing a miniscule amount of scientific realism (that requires significant scientific knowledge to appreciate anyway) -- for purposes of advancing a story -- and sacrificing more significant amounts of everyday realism (such as realism concerning the # of women admirals in the military) which is only engaged in for political purposes.
Sacrificing technical/scientific realism to advance a story is unfortunate but sometimes necessary. Sacrificing basic/everyday realism for political purposes is both unnecessary and unfortunate. That's the difference.
Bioware should not cater to people who are terrifyingly ignorant of statistics and science. If you think "blue skinned aliens that look like sexy human women" is "sacrificing a minuscule amount of scientific realism", then ... well, I'm not sure how to break this to you, but you're completely wrong. Almost everything related to "science" in Mass Effect is as realistic as you, right now, getting frustrated in reading my post, transforming into the fictional DBZ Super Saiyan.
Beyond that, the bolded part of your post - "in numbers that are much greater than what tends to be observed in reality" - is nonsense. First of all, it's a statement that's so general it doesn't mean anything. Observed in reality where? Because reality isn't a simple random sample of some general population. It's rare for people to have cancer. But it's not impossible to meet - in one room - a majority of people who happen to be cancer survivors. In reality. That doesn't mean reality sometimes has become unrealistic. Second of all, who is doing the observing, and where? Depending on the actual IRL military right now, if the proportion of women in the army reflects American figures, the amount of women would be over (or under) represented. In fact, you mention race. Why should the race proportion reflect the American military and American society? Why not China? You're acting as if it's some inaliable truth that some arbitrary country in the 2015 has set the absolute and eternal standard for population distribution in the army... but why?
If every single moment in every single came somehow was proportionally representative to broad population statistics, the whole game would be so incredibly "unrealistc" that you should be up in arms about it. But, of course, you're not, because your (clearly ignorant) understanding of science and statistics is very likely not the reason behind your objection here. If it is - and if realism matters to you - then it's time for you to start studying. Because you can't cry realism on the one hand, and yet plead ignorance to science and statistics, particularly when your alleged political/social realism relies on, you guessed it, science (and statistics).
If you think that, somehow, women are less fit to serve than men (because of strength or athleticism, or whatever), you've got to two bases for belief, which is an emprical claim: the embarassingly ignorant one where you've read and studied nothing, and are advancing an opinion with no reliable information, or an actual position ground in some science. Now you may well want to be ignorant. That's your business.
But if you want to make a realism claim, and you want it to be taken as something other than a joke, then it might behoove you to actually inform yourself. And once you do that, trying to draw a distinction between the science of Mass Effect and gender disparity on the lines of "only people who know science will care and it's miniscule anyway" (the second being, again, totally ignorant and in fact absurd to say) becomes an evident joke.