After lots of speculation, Namco has finally confirmed that Tales of Vesperia has remained an Xbox 360 exclusive in the West because Microsoft paid them to keep it that way.
A PS3 version of the game did eventually release in Japan, but outside of Japan it's only been released on Xbox 360 - more recently via Games on Demand.
"Microsoft paid for the exclusivity the same way Sony paid for having Heavy Rain only on PS3," revealed Namco Bandai's community manager Charlotte Toci.
When Tales of Vesperia released on PS3 in Japan it almost doubled the sales of the Xbox 360 version - even though it was released over a year later. Tales of Xillia, the next game in the franchise, will be PS3 exclusive.