I guess it's possible that a "hack gap" has something to do with it, but think the easiest explanation for why Stu Bykofsky's "We need a new 9/11" column hasn't attracted the same kind of sustained criticism on the left that, say, Markos Moulitsas's "screw 'em" reaction to the deaths of military contractors in Iraq attracted from right-wingers is that nobody knows who the hell Stu Bykofsky is. There was plenty of sustained outrage when Ann Coulter called John Edwards a faggot, you may recall, because Ann Coulter is famous, and it's smart politics to tar the conservative movement with offensive comments made by one of its best-selling authors. Similarly, Kos's comments about the deaths in Fallujah came at a moment when the left-blogosphere was just emerging as a significant player in liberal politics, with Kos as the acknowledged king, and so his vile (though retracted) comments made ideal fodder for the left-blogosphere's many critics. Whereas Bykofsky is a Philly columnist who mainly writes about local issues (see here, here and here for representative columns), who seems to have basically liberal politics and no national reputation to speak of, and whose connection to the Vast Right-Wing Conspiracy appears to start and end with his support for the War on Terror. Which makes him a pretty lousy target for sustained left-wing outrage.
Ross Douthat is a former writer and editor at The Atlantic.