My own personal theory is that there are two collective phenomenon at play here:
1) There's a self-cyclical force here where some people think brogramming is a label some people use non-ironically, so there are things like marketing materials developed specifically for it, which by definition will be exclusionary and sexist. This material further spreads the idea that "brogrammers are real" and everyone gradually forgets that nobody is actually this ridiculous.
2) There is a fear among programmers that our wonderful merit-based community accepting of all genders, cultures, and creeds -- which it is, really -- is going to turn into Phi Delta Toolbag overnight. For a lot of us, myself included, we've never been one of the "cool kids" and found computers and technology a much better fit for our introverted personalities. And suddenly these pink popped-collared polo shirt sunglass-wearing monsters are going to take that away from us.
Anyway, I understand why the women at UPenn would be offended by the "brogrammer" term, sometimes you just don't want to be associated with a term even if it's satirical. But are there actual brogrammers out there being sexist, or is this an overblown issue?