In my mind, it's clear that it isn't 100% a moneyhat. Capcom was likely shopping around for a way to avoid having to do a PS3 version once they figured out how much it would cost, and looked to the Wii as having similar assets to what they had already developed, so that they would not have to spend that much for Tri. Remember that it wasn't until around the year 2008 that Monster Hunter became a really big deal, well within the timeframe for when Tri came to the Wii (development-wise), so it likely wasn't really worth moneyhatting before that. Nintendo became much more accommodating as the development process went on and MH's popularity increased apace, developing things like the Classic Controller Pro, and running the Western advertising campaign. It was easier for Nintendo to push for 3DS exclusivity for the next numbered entry after that point.
tldr: it wasn't Nintendo just knocking on Capcom's door with a sack of Yen in hand, but it does involve significant input on Nintendo's part, more than they've done for other games or other third parties in the past.
Monster Hunter: pissing me off since 2010.
