"It was easier developing for the Xbox 360 ... if you sign an exclusive contract with Microsoft (you won't release it on other hardware for a year or similar), they will give you a lot of cash for development," read a Japanese developer's post (the original post has since been removed), translated by Sankaku Complex (site NSFW). "As a result, first you develop for the Xbox, reducing development costs. But the Xbox version won't sell [in Japan]. So they port it to the PS3 ... it's cheaper as you already have the game done."
Though they didn't work on it, the developer claims to have seen this policy in practice with Tales of Vesperia. As Kotaku points out, it's quite possible that the dev did see such a practice on Vampire Rain, a game the mystery developer says they worked on.