As has already been stated in the thread, Gaiman has stated he's a Miyazaki fan and he's even been involved in Miyazaki's movies himself as an English translator for them. He may not have set out to create a word for word rip off but if he had seen Laputa before creating Stardust, it's very plausible that he incorporated different themes and motifs from Miyazaki's movie into his work, similar to how Tolkien had incorporated elements from Richard Wagner's operas into LOTR. He may not have intended a direct rip off and he took Richard Wagner's concepts into very different directions, but he clearly borrowed the concept of magic rings that turn the user evil from Richard Wagner. Likewise, Gaiman may not have set out to directly rip off Miyazaki, but he's clearly getting his influences for a girl from the sky with a magic stone being chased by various factions for control of its power and flying pirate ships from Miyazaki. These similarities don't make Gaiman bad and I quite enjoyed Stardust but they don't make him original either.