This should be obvious to anyone, but it is not quite as obvious as it seems. Similarity in relationships is not always about liking the same things. People can share favorite TV shows, artists and movies with their potential partners yet still find themselves completely incompatible with them. Similarity is essential when it is a shared mind-set or viewpoint, and much less important when it is merely shared periphery factors.
While couples often seem to enjoy the same music and movies, it is much less a result of mere coincidence and mainly a result of shared tastes and world views. It is more likely that a long-term couple would meet each other, completely unfamiliar with their tastes, and grow more similar over time than it is to find a couple that grew attracted because of shared direct interests.