It’s the notion that comforts many a TV showrunner: Abandon broadcast TV and leave your ratings worries behind; all cable cares about is quality.

But as those behind some critically acclaimed cable shows are being reminded, you can run from ratings worries but you can’t hide.

“Rubicon,” one of last summer’s best-reviewed new cable series, was canceled by AMC on Nov. 11 after one season. And “Terriers,” one of the fall’s best-reviewed new cable series, is on the ropes at FX, its audience well below a million viewers overall, with a microscopic rating in the 18-49 demo.

Each series debuted to positive reviews and then improved creatively as their freshman seasons progressed, earning the kind of viewer passion that made success stories out of network-mates like AMC’s “Mad Men” and FX’s “Sons of Anarchy.”

But with the “Rubicon” cancelation came the reminder that when it comes to ratings, even cable — at least basic cable, as opposed to subscription-based channels like HBO and Showtime — has its breaking point.

“What was presented to me by AMC — who, by the way, I really liked,” says “Rubicon” showrunner Henry Bromell, “is that it wasn’t the (overall) numbers that was the problem for them. It was the fact that the demographic skewed old. And since AMC is advertising-based, not like Showtime or HBO, they need those ads. That’s their business, and they couldn’t get them.

“They started talking about these numbers, and it had never come up before in discussions, because it had never occurred to them it would happen. They were flummoxed.”

And so even though “Rubicon” actually topped ballyhooed AMC series “Mad Men” and “Breaking Bad” in viewers for a series premiere, the conspiracy-minded series became the odd man out on the cabler, especially after “The Walking Dead” launched as a relative ratings powerhouse with 5 million viewers.

“Apparently the discussions over there really did get anguished,” Bromell says. “I think theygenuinely loved the show, and they wanted to keep doing it. And they thought it would hurt the image of AMC not to continue with it. But the advertising guys were saying, ‘We love it too — but we can’t sell advertising for it.”

Trying to avoid a similar fate is “Terriers,” which fell to some 540,000 viewers and a 0.2 rating in 18-49 in its Nov. 10 airing before showing relative signs of life with 725,000 viewers and a 0.4 on Nov. 17. Its season finale on Dec. 1 drew 784,000.

Showrunner Shawn Ryan will take the good news where he can get it, but “Terriers” still has what Ryan calls “an uphill climb” as he tries to convince FX prexy John Landgraf that the show’s growth potential makes it worthy of renewal.

“I understand the reality of the situation,” Ryan says, “and I understand that John and (his colleagues) run a business and they have people they have to answer to in terms of profits. “But it seems they’ve done a good job of making the company profitable, and maybe there’s room for us (to grow). We’ll make that case.”

Ryan, who previously made seven-year enterprise “The Shield” a defining show for FX, says he was never under any illusion that he didn’t have to worry about audience size.

“I never considered that the promise,” he says. “Obviously, if you have ads in the middle of a show, the ratings are going to matter. (But) at a place like FX, quality is really important, and I think that they’ve shown greater patience than most ad-supported networks.”

To be sure, cable remains immune from the kind of summary execution that befell the fall’s top-reviewed broadcast series, “Lone Star,” guillotined by Fox after two weeks. Ryan points out that FX rode out the ratings-challenged first season of “It’s Always Sunny in Philadelphia,” which will complete its fifth campaign this month. And although FX has parted ways with “Damages,” the cabler stuck with the Glenn Close starrer for three seasons, all the way through April’s season finale (900,000 viewers, 0.2 demo rating).

“There’s a certain threshold that really does matter to them,” Ryan says.

DirecTV made a deal with Sony Pictures TV to keep “Damages” alive for two more seasons on the satcaster’s 101 Channel, but senior entertainment and production veep Chris Long of DirecTV makes it clear that “Damages” isn’t seen as a charity case. Even as it prepares to exit the business of saving shows on the brink of cancelation ( Daily Variety , Nov. 22), DirecTV is planning a big marketing push for the new episodes of “Damages” and expects the show to perform.

“We think there is an enormous amount of value for us,” Long says, adding that it’s “naive” to think that audience totals don’t matter for non-broadcast TV shows. “We get Nielsen ratings,” he says. “We do a seven-day Nielsen rating, and you can’t never look at the audience. Then you’re programming TV for yourself.”

Cable and broadcast still remain two distinct worlds — in fact, Bromell thinks the gap between the two has “widened.” Cable remains a place where a showrunner has much more freedom, though as Bromell learned the hard way, there are no guarantees.

“You have to have something in your head that you think is really cool,” Bromell says, “and you fight tooth and nail to defend it — knowing, in the back of your mind, you could be wrong.”