Why is it that designers have managed to make this the accepted (and expected) reaction to this kind of exploitative stunt, but not writers?

There was a small kerfuffle over HuffPo's treatment of volunteer contributors back when Aol bought them, but it seems to have fallen completely off the radar.

Is it just a matter of publicity and convincing everyone in the field not to do free work? Or do we as a society really value the written word that much less?

(For the record I support both designers and writers getting paid enough to make a living on their work. To borrow from Mike Monteiro: "Fuck you. Pay me.")