The Enquirer prints lots of absurd stories for the entertainment value. They also occasionally cover stories that the "mainstream" press doesn't want to touch. Remember, they exposed the John Edwards-Rielle Hunter soap opera, they broke the story of Jesse Jackson's "love child".
They have lots of lawyers who are expert in libel and slander laws and have to be careful about exactly what they say that could be considered defamation of a living person unless they have evidence to backup what they say.
Yep, they also broke the Rush Limbaugh Drug Ring investigation, the day after the story broke he checked into rehab to avoid jail time.