It is, as you note, the only bit people who don't read the article will read. (And as it happens, I did read it, but don't let that stop you from jumping to conclusions.) That includes people who don't click through from the HN front page, but the message will lodge in their brains regardless.
It is also, presumably, what the author feels is a good one sentence summary of the article: he cannot hire women, because it is illegal... so he has no choice but to hire men only from now on (subtext: stop blaming him for the 15-1 gender imbalance at his company, nothing to do with him, honest).
Another way of putting this: if the author knows full well that it is NOT discriminatory to employ women, why did he lie to us in the article's most prominent sentence?
