eMarketer predicts that spending on online video ads will rise 42 percent next year to $1.5 billion—but for individual networks, it’s still going to be “digital dimes” for offline dollars, to borrow NBC Universal (NYSE: GE) CEO Jeff Zucker’s line about the business of web video versus TV.

So while networks are concerned about alienating web viewers who have turned to online to avoid the heavy rotation of ads, they also acknowledge that the high premiums they’re getting for their internet programming is not enough to sustain them. Speaking to the WSJ, Andy Heller, vice chairman of Time Warner’s Turner Broadcasting, warns: “We spend billions of dollars buying and making these programs. And if we give this stuff to consumers for free with limited ads, it’ll go away.”

Of course, the worries are largely eased at the moment by the fact that online video ads can’t be skipped. But it’s hard to believe that just as pop-up blockers came into existence, there won’t come a time when viewers can bypass online video ads as well.