And I think I have my answer:

Last week, researchers in London reported that they had analyzed nine randomized studies of aspirin use in the United States, Europe and Japan that included more than 100,000 participants. The study subjects had never had a heart attack or stroke; all regularly took aspirin or a placebo to determine whether aspirin benefits people who have no established heart disease.

In the combined analysis, the researchers found that regular aspirin users were 10 percent less likely than the others to have any type of heart event, and 20 percent less likely to have a nonfatal heart attack. While that sounds like good news, the study showed that the risks of regular aspirin outweighed the benefits.

Aspirin users were about 30 percent more likely to have a serious gastrointestinal bleeding event, a side effect of frequent aspirin use. The overall risk of dying during the study was the same among the aspirin users and the others. And though some previous studies suggested that regular aspirin use could prevent cancer, the new analysis showed no such benefit. Over all, for every 162 people who took aspirin, the drug prevented one nonfatal heart attack, but caused about two serious bleeding episodes.

http://well.blogs.nytimes.com/2012/01/16/daily-aspirin-is-not-for-everyone-study-suggests/