Thing is, Joffrey was created BEFORE Draco and his appearance (as described by the books) fits with Jack Gleeson. It's just amazing coincidence that he and Draco seem alike (though Joffrey is worse than Malfoy ever could be).
The book Joffrey doesn't come across like (either the book or film) Malfoy though...
Caligula, yes, Malfoy, no...