It's very likely that Nintendo moneyhatted Capcom for time-exlusive, similar to how MHTri.
Expect to see MH4Enhanced on other platforms in 2 to 3 years after the 3DS release.

 Look I'm just looking for reasons for why it wasn't announced last night. Who knows it could be true.

It wasnt announced last night because Nintendo gave capcom money, its quite obvious. If it is comming to Vita capcom have obviously done a deal with ninty to keep that quite for now, this way the 3DS could benefit even more from pre-release hype as monster hunter fanatics are likely to buy  the system under the believe that this an exclusive, especially with christmas comming up.

As for the idea of the game not being suitable for the Vita, the platforming elements looked a bit tricky (mainly due to the camera), but not enough to warrant the idea it can only be done with 3D. Actually it is very easy to se the fields of distance and which platform follows which. On top of that as RolStoppable mentioned, the video was cleary edited to be cinematic and mayb not even in-game.  the camera is not gonna be as wild as it was in that video..

I don't have enough facepalm pics for this thread...

Wow , this guy is serious, better leave this thread and go sit in the corner to perserve my positive karma.

Some or much of that will likely end up in the actual game. The only thing i found incredulous was how the monster destroyed those pillars, thus altering the environment in a way that would make it impassable for other players in co-op mode, but i am willing to believe a more involved platforming/mountain climbing/mounting the monster's head to do damage is forthcoming

Where were the fast platforming parts in the video?

Most of the Megaman games have trickier jumping going on than anything I saw in the vid.

Wow...MH4 is not coming out on the Vita!!! That's like a kick in the teeth for Sony!!! Those who think MH will not influence portable sales are fooling themselves. MH was one of the main reason why PSP sold so well in Japan. A major coup indeed for Nintendo and the 3DS. IMHO Nintendo's pre-TGS outshown Sony Vita's TGS presentation.

Well this and nintendo paid them are the to best probable reasons I think it wasn't announce. But this reason seems more interesting(funny) to me. Wont it be funny if vita had all that power but lost a major exclusive because of no 3d effect?XD

But seriously, you wanna bet capcom would at least say 3d is one of the reasons they brought it to 3ds.

You know Sony is working on an ugly addon to add 3D effects to the Vita, that makes it twice as big and impossible to hold. Sony is probably adding another screen as well, as MH4 will probably need two screen to play, because of those "fast paced platforming jumps".