Now sit right back and you'll hear a tale -- and it's a tale you've heard before.

News came last week that Warner Bros. has given the green light to a new movie based on the '60s sitcom "Gilligan's Island." There also were announcements that remakes of Stephen King's horror story "Pet Sematary" and the lowbrow farce "Police Academy" are also in the works, and talk that Robert DeNiro may be interested in making a sequel of his 1988 bounty-hunter comedy "Midnight Run."

It's nothing new to point out that movie studios like to copy from previous works -- whether it's books, old movies, TV shows, video games or toy lines. But rather than rehash the usual complaints about rehashes, let's consider why everything old becomes new again in Hollywood.

The answer is the same answer for any question regarding Hollywood: money.

The movie industry is all about avoiding risk, and there's nothing riskier than an original screenplay. When a writer pitches an original screenplay, he or she has nothing but the words and a resume to convince a movie studio to cough up some money.

But when a writer or producer takes something that's adapted from another source, the studio executive has a ready-made image in mind.

For a franchise like "Gilligan's Island," for example, there's the image of Bob Denver in that goofy hat -- and it doesn't take a lot for an exec to then picture Michael Cera as Gilligan or Beyonce as Ginger (both names suggested by Sherwood Schwartz, who created the original series). And if you can hum the theme song before a frame of film has been shot, you're halfway home.

An established title like that can fire up the public's imagination, too. Several entertainment bloggers started making speculative casting lists. (My picks: Salt Lake City's own Patrick Fugit for Gilligan, Kurt Russell for the Skipper, Don Cheadle for the Professor, Christina Hendricks of "Mad Men" as Ginger, Zooey Deschanel as Mary Ann, and maybe James Gandolfini and Marisa Tomei as the Howells.)

And it's not as if they're rewriting Shakespeare or something. "Gilligan's Island" might be a fondly remembered sitcom, but even its fans will acknowledge it wasn't highbrow entertainment. It's not like the movie is going to be much worse -- though never underestimate Hollywood's talent for making something bad into something momumentally terrible.

Sometimes a remake can improve on the first effort. John Huston's classic 1941 version of "The Maltese Falcon," starring Humphrey Bogart as Sam Spade, was not the first time someone tried to turn Dashiell Hammett's detective story into a film -- but it was the best.

A remake, particularly in science fiction, can take advantage of advances in special effects. J.J. Abrams' "Star Trek" was a polished reboot of the beloved franchise, embraced by old-line Trekkies (except for my colleague, Vince Horiuchi) and newbies alike. And this December's "Tron Legacy" could be, if the fanboys' dreams come true, a case of a franchise catching up to the technology it needed to fulfill its promise.

For audiences, a remake of a familiar title is a dicey proposition. The franchise might not be as well-remembered as its producers think, and a new movie will fail to connect with a new generation. Or it's so beloved that any monkeying around is rejected by the core audience. In the case of last year's bloody-awful "Land of the Lost," both things happened at once.

We won't know how good "Gilligan's Island" or any of those other remakes will be until we see them. Each time the house lights go down, there's always the hope that the movie about to start will be fresh and interesting -- even if its source material is from the cheesiest old sitcom.

Sean P. Means writes the Culture Vulture in daily blog form, at blogs.sltrib.com/vulture