Super Smash Bros: The Difference Between Wii U & 3DS Versions
"From an artistic standpoint, when we’re looking at these high detail environments that we’re creating, we now have to go in and work on all of those little things, because as you can see, if you don’t put in the attention to detail they look flat and lifeless."
That’s not all, however, the Wii U version will enable "increased fidelity and detail" while still pulling the camera out and keeping it looking as good.
This means Sakurai and his team has "the ability to create things on a bigger scale".
As a result of developing for two platforms, however, Sakurai suggested there are limitations, including the dream of levels from Super Smash Bros Brawl (from the Wii) appearing in the latest Super Smash Bros game.
via Super Smash Bros: The Difference Between Wii U & 3DS Versions - NowGamer.