For Purposes of Comparison...
I wondered if Girls' ratings were good for HBO. After all, a lot of people might watch programs later, on demand, and maybe HBO defines "good ratings" pretty generously.
But last season's finale of Game of Thrones attracted 4.2 million viewers.
And that's a hit, but I don't even think that's a Big Big Hit. Just a Hit, or maybe even a Big Hit. Wikipedia tells me that The Sopranos
grew in ratings from a starting season average rating of 3.46 million to a final season average of 8.42 million. Entourage
, which for some reason was well-liked, got ratings in the 2.4 million ballpark. Homeland
, a premium channel sorta-hit on the less-subscribed channel Showtime, garnered 2.4 million on a randomly chosen night.
I suppose it's great that Lena Dunham is a female television auteur
and I suppose the boosterism is all but inevitable, but you're quite right, it's simply not the phenomenon it's being portrayed to be. What it seems to be is a hit among the specific people whose ratings matter.