With a head start in fundraising and organization, Barack Obama outspent Hillary Clinton throughout the Pennsylvania primary battle. And yet, in the final week, strategic use of advertising allowed Clinton to reverse most of her losses, seize a decisive victory, and revive her campaign.

Driven by internet donations, fundraising in 2008 has dwarfed the money hunt in previous campaign cycles and pumped up the campaign industry. So it's especially strange how, until recently, campaign ads were the dog that didn't bark.

Ads—which are, in theory, the point of all that fundraising—have had little impact on most of this cycle. John McCain sewed up the Republican nomination despite having little cash for commercials. On the Democratic side, Clinton has stayed close to Obama despite his significant financial edge—at times, a 2-to-1 advantage in money raised.

A big reason for this apparent paradox is the fact that voters this year are more interested in presidential politics than they have been in a long time. Generally, what is referred to as "free media"—news stories on TV and radio and in newspapers—deliver candidates' messages to engaged, avid voters, while paid advertising is needed to reach the many others who pay little attention to political news.

This year, with more Americans actively following the campaigns, the weight of influence has been tilted toward the news media. It got to cover the intense drama of Obama's crowds, Hillary's tears, Bill Clinton meltdowns, and the many debates.

Candidates still spent heavily to broadcast ads, but they were usually bland and reflected little of their intensely combative dialogue on the campaign trail.

Clinton's early ads, for example, mostly featured jobs and other kitchen-table issues that polling identified as convincing, while Obama's ads seemed aimed mainly at his converts, often using music and fast-paced editing to convey the excitement of building a movement.

Obama's Christmas ad showcased his family; Hillary's showed her wrapping presents with labels like "Alternative Energy" and "Universal Pre-K."

Obama's ability to fire up his base often trumped Clinton's focus on using issues to woo undecided voters. His ads appeared to be secondary to his campaign's top-notch ground operation and mastery of the Web—and his own impressive ability to draw throngs.