But in all seriousness, this game is exclusive for two reasons:
1. Sony and NIS have built a rather close relationship over the years. NIS has been using Sony's PhyreEngine for all of their PS3 releases, and they were one of the first developers to get NGP development kits. They actually got NGP kits before they got 3DS kits, unlike most other devs, and this preferential treatment is the reason why they support PS2/PS3/PSP so heavily. Unless this changes, their products will usually be made first and foremost for Sony's platforms.
2. Much like most other niche Japanese developers, a majority of NIS's sales come from Japan, so it's not surprising they'll primarily support the console with the best software sales in the region. They could branch out and release on 360, yes, but they'd be adding a very small percentage of sales to their total, for the cost of retooling an engine designed entirely around the ps3 to another platform. It simply wouldn't be worth the added costs. At least that's what they seem to think. Plus, by going multiplatform, they'd be sacrificing some of that support mentioned above.