Question is, how much support did the original DS get from 3rd parties? I'm not sure at all, but from what I've heard, it was mostly Nintendo games that sold and and 3rd party support was rather poor. If this is the case, why would Japanese developers support the 3DS? It's probably not gonna sell as well as DS. Is your "3DS getting more support from J-games"-argument based on the fact that Vita isn't no PSP?
I believe that 3rd party support will be strong for all next gen consoles; it won't be like this gen when Wii only got shit ports.
And having a strong handheld console doesn't automatically mean better support for your home console. Case in point: the Game Boy series. This line up of HW dominated the handheld market from 1989 to 2004, coinciding with the N64 and GameCube; arguably Nintendos worst supported systems, and definitely worst selling home consoles. Going by your logic as formulated in the OP, these would have been great days of 3rd party support for Nintendo. And yet, they are remembered as the Dark Ages of Nintendo...
I'm on Twitter @DanneSandin!
Furthermore, I think VGChartz should add a "Like"-button.
