The NY Times has an article on Neuroscientists and Marketing. Like the answer isn't already obvious: fear.
Playing on fear hits on the second level of Maslow's hierarchy of needs, safety. This has to be satisfied before love, self-esteem, or self-actualization. Targetting this hits us at the mammalian level, even below the monkey. Only raw physical drives come before this. This is why SUV's are selling so well. Car buyers have been convinced that SUV's are safer. In fact, they're not--their center of gravity is too high for their wheel base, and their size and weight makes them less maneuverable, making accidents more likely and more deadly when they happen. But the perception, fostered by advertising, has made them a runaway success.
This also explains why politics has been so warped since 9/11. All those alerts are scaring the hell out of people who haven't applied a little statistical perspective and realized that even in 2001, your chances of being killed by a terrorist were far less than being killed by in a car crash. By the same reasoning, we should all stop travelling in cars. But rationality doesn't even get a chance at this level.
It also explains why Democrats are more frightened by footing of 9/11 than Republicans. Republicans actually think Bush is doing a good job against terrorism, while Democrats are aware that the invasion in Iraq had nothing to do with terrorism, and may make the problem worse by aggravating Islamic paranoia. In other words, Democrats see 9/11 as a threat which has not yet been dealt with properly.
Understanding the role of fear in people's choices explains a lot of things: the War on Drugs (fear of gangs), McCarthyism (fear of Communism), Fundamentalism (fear of uncertainty), and knee-jerk patriotism (fear of foreigners.) Whenever you see people acting like lemurs, it's a pretty good indication that this is what's happening. And the best advertisement of this is the 6:00 news, where no news is good news, and the entire program is spent on statistical anomalies. This was also the real conclusion of Bowling for Columbine; the guns don't help, but other countries have almost as many guns as the Americans. What they don't share is the irrational fear.
Advertising just rides on the coattails of bad journalism.