How it happened was that Harvey Weinstein promised Quentin Tarantino, in his contract, that Tarantino would be allowed to shoot and release the unexpurgated script. When it came down to editing the film, Miramax realized that he'd made a 3+ hour kung fu movie, and began to get cold feet. As a compromise, and in keeping with the letter of the contract (if not the spirit), Weinstein and Tarantino agreed to divide the movie in half and release it in two chapters. Voila, Tarantino got to keep total creative control and release it under Miramax (his loyalty to the studio he helped put on the map shouldn't be discounted), and Harvey got to double his gross by making people see two movies instead of one AND maintain Miramax's artistic cred by not chopping a 3 hour movie into one 90 minute movie.
Worked out great for them, but I'm still shelling out $20 instead of $10 for a movie I would have gladly sat 3 hours for.