“The series did start out on Sony platforms, but it’s just realistic to think that it can’t continue on one platform forever,” says Tsujimoto. “With Monster Hunter 4, it actually just came down to timing - we were developing a new Monster Hunter and the 3DS hardware had just come out, so we figured it was probably the best platform for us to develop it on. You have two screens, with action on top and menus on the bottom, and there’s the 3D view as well. It just made sense to put it onto 3DS.”

Plus, why MH 4 is not on Wii U

“The way that we work with Monster Hunter games is that we see them as single entities, so we don’t develop for one platform and then think about porting it to another platform. The situation with the 3DS and the Wii U is that we wanted people to play this game a lot, so that’s why we have taken this [multi-platform] approach with Monster Hunter 3 Ultimate. But it doesn’t mean we’ll do that with new entries.”

Sauce

There's the first-mover advantage, plain as day.

Plus, you know these guys have been enjoying their blockbuster success on PSP... but they've gotta wonder... there are an awful lot of DS systems around. If you're gonna grow, you need to a platform where you aren't the only system seller.

Monster Hunter 4 is so going to Wii U too.

Can't wait to play Ultimate :) - good or bad, it's on the to do list for so much time!

Why? easy
Capcom looked at the Hw charts and decided to support the most successful co. out there

IGN also has this story about MH

lol yes this does in fact mean MH4 is going to be ported to another platform and hopefully WiiU where I will be getting!

not going to get this on 3DS

Translation: "We would've had the game on the DS if it could've handled it. So the 3DS was a no-brainer."

Why do I have a feeling that they'll probably port MH4 to WiiU anyway?  Oh, because it's CAPCOM.  And they LOVE to port everything **waves at MEGA MAN and RESIDENT EVIL.

...says a third-party? When did that start?

Since the Big BANG.