As news consumers gravitate toward mobile in troves, the question at many media companies is whether dollars, not dimes or pennies, will follow. An audience-inventory problem persists in mobile because supply far outweighs advertiser demand for mobile real estate. The number of players — from local media outfits to Web giants like Facebook and Google — has driven CPMs in many cases lower than desktop, regardless of the traffic increases. A special report by Patrick Duprey.