I haven't been following the whole Girls hub-bub too much, but I can't say I really agree with that article on a few points. No doubt a lot of TV is racist/sexist, and yes, more consistent attention should be paid towards that. However it seems one of the reasons people are still harping on this particular program may be due to incidents like these:
Also I'm not sure blaming HBO is really the answer either considering some of the other shows they've broadcasted that have directly encountered the issue of race in an intelligent/engaging framework (e.g. The Wire, Oz, Treme).
I'll be the first to admit I haven't been following it too closely either. The responses themselves are ugly (at least, how they are presented in your quote, I haven't seen the actual responses), but it does not make the show itself more or less racist.
As for putting the blame on HBO, I don't think that is the point. I think the point is out of all the TV that we see everyday, why did Girls attract such a reaction, when a multitude of shows fit the same archetype. I don't argue this is a systemic problem; but it is one one unique to Girls, so I don't feel particularly motivated to blame on Girls.