However, I can't help but notice that, for example, a number of films released by Disney/Pixar, Dreamworks and other mainstream childrens' film studios bear curious resemblances to each other: Antz and A Bug's Life, The Wild and Madagascar, Finding Nemo and Shark Tale, WALL-E and Robots.
Another example is the run of post-apocalyptic road movies including Zombieland, The Road, The Book Of Eli, Carriers and so on.
The Asylum released their own version of Sherlock Holmes - with pterodactyls! - but at the same time the BBC released a present-day TV mini-series Sherlock. The BBC did exactly the same thing in 2005 with Casanova, starring a pre-Doctor Who David Tennant, around the time of the Heath Ledger movie of the same name.
When a movie or franchise proves successful, you get not just one lookalike but a flood: the success of Harry Potter led to a run on the children's literature bank with adaptations of C.S.Lewis, Susan Cooper and many more. Vampire movies have been on the ascendant for some time but in the wake of Twilight you can be sure there are plenty of sparkly lookalikes still to appear. And why is it both Tom Cruise and Kate Winslet appeared in Nazi movies so close together? Meanwhile, my wonderful guest blogger Amanda mentioned Paranormal Entity but somehow omitted Paranormal Calamity, Abnormal Activity and Paranormal Effect.
Sometimes the doppelganger isn't quite what you'd expect: I vaguely remember a reviewer pointing out that Super Mario Brothers turned out to be about dinosaurs - a departure from the theme of the computer games which, they speculated, might have been an attempt to cash in on the success of Jurassic Park.
Releasing movies that resemble other movies works for the same reason we go to see sequels and re-makes, because a good movie leaves us wanting more. Right across the industry, producers are whispering to each other in smoky speakeasies: "Warner are releasing a mummy/ insect/ robot/ octopus/ supermarket trolley movie next Spring - quick, can we get one out too?"