I could be wrong here, but I think Nintendo money-hatted Capcom for Monster Hunter, so it would only be their decision if Sony ponied up more dough than Nintendo.
For some reason I seem to recall Sony and Capcom having some sort of feud over it too, if someone else can refresh my memory on that, it would be great.
Seeing as the 3DS is putting up crazy numbers in Japan (over 20 million I believe), I'm not sure bringing MH4 to the Vita would do much for them. Sure some people would buy the Vita just for that and it could probably sell well, but most people would just go "Why buy another console for a game I can get on the console I already own?" So in that aspect, it isn't really about "would it sell less because there are other hunting games on the system" and more "would it sell less because the Vita isn't nearly as strong in sales"







