Let me re-iterate myself: I didn't mention any specific attribute, not to say specific gender or ethic groups. So, what you are saying here is probably not a natural interpretation to draw from my question.
I do agree with the cultural fit part though. It's subjective and easy to manipulate to what direction as convenient to the company.
Talk about "dumb", I don't think sane companies will ever hire anybody who they considered as "dumb", because it's counter-productive. However, it's possible that a certain group have a slightly lower bar. They are still good, but just not as selective as their counter part. As long as it's good for the company's public image, morale, etc, they might want to make this trade-off.
Does this policy not uncommon in the industry? -- Is essentially my question. Please note that this doesn't necessarily mean that certain group(s) are superior/inferior then the other group(s). This simply means the general public confused the population as general population, instead of number of candidates. So that companies might want to skew the graph a bit to make it composed more like general population to please general public, media, whatever.