Romney's attack on PBS was no accident or gaffe. It was a calculated attack and bitch slap directed not so much at Bird Bird, but at the guy who was supposed to moderate the so called Presidential debate: Jim Lehrer. The not so subtle message to Lerher was, "TRY to act like a journalist and put me on the spot during this debate, and I will eliminate your job when I am President!" However, Romney had nothing to worry about on that score because Lehrer got the Republican message a long time ago. In fact, Lehrer stopped being a journalist back in the 1990s.
I used to watch The News Hour because it gave a lot more background information and analysis of the major news items than the worthless national outlets ever did. But when the Republicans came to power after the 1994 Election, things began to change on The News Hour. Republicans screamed that the PBS news division was a haven of lefties, and there needed to be more "balance" on PBS. Republicans threatened PBS funding, and, lo and behold, The News Hour began to conform to Republican views on political balance.
One way to find political balance is to neuter the journalists. Eunuch journalists will present the "he said, she said" argument and do nothing to correct the record to the story. This is what Lehrer does.
Lehrer would bring on guests to discuss some news topic, and he would have them go at with little or no import from him. I remember one terrible news segment on sex education and HIV-1. No medical experts were brought on to educate the public. Instead, some social conservatives who were invited spread the lie that condoms have pours that allow for the HIV-1 virus to pass through, so condoms were actually worse than useless at preventing the spread of AIDS. Lehrer did not bother to correct this lie.
Basically, the News Hour is just a more civil version of the old CNN show Crossfire.
So why did Romney threaten a good little neutered lapdog like Lehrer? Probably habit more than anything else is my guess. Besides, as Bill Maher says, the low information voters probably think that we spend hundreds of billions of dollars on PBS.