On one hand, stories not like other products in that they not interchangeable. On other hand, stories be interchangeable. Both can be true.
Stories are like dreams for groups of people. They arise out of societal needs and reflect elements of cultural experience. Every big event always followed by books and movies, and not just because topical things sell. They am way for society to digest said event. After every war, there am war stories. Vietnam gave us characters of Rambo and The Punisher as way of embodying stereotype of dangerous PTSD-riddled Vietnam vet. It interesting to note that to my knowledge this has remained consistent part of Frank Castle's backstory, with the consequence that he ages in real time while rest of Marvel Comics am stuck in comic-book time.
Anyway, in this sense stories am not interchangeable products. They arise out of specific circumstances and am received in specific circumstances. Whether success or failure, results am impossible to duplicate -- it like trying to step into same river twice. This explain why nobody has been able to duplicate success of Terminator 2, despite all the money thrown at the problem. Terminator-2-shaped-hole already filled by Terminator 2, thankyuvurrumuch.
At the same time, acceptable substitute for specific stories exist, otherwise genres would not exist. Cultural zeitgeist aside, people tend to like certain kinds of for their own personal reasons. The Witcher may not be perfectly-interchangeable with The Hobbit but fans of both see more similarities than differences.