(FORTUNE Magazine) – Julie Roehm has more than $2 billion to spend this year, and the way she’s been spending it worries executives at News Corp., the Washington Post Co., and virtually every other media company on the planet. As Chrysler’s director of marketing communications, Roehm, 34, oversees a budget that Advertising Age ranks as the sixth-largest pool of ad dollars in the nation. She decides how many minutes of the carmaker’s commercials appear on networks and cable channels nationwide and how many pages of its ads turn up in magazines like this one and newspapers such...