It seems to me that no volition is needed on the part of journalists: journolists need sympathetic and sensational stories, but a sensational story is more likely than an average story to be false. (Extraordinary claims requiring extraordinary evidence...). Combine this with the selection pressures on journolists for cutting corners in pursuit of a story/deadline, and you can pretty much guarantee that of any story type a disproportionate number of the biggest stories will be exaggerations published by unscrupulous reporting. This mechanic holds for every story type, not just rape.