What the hell does toon shading have to do with higher quality gameplay? Hell, if anything, the toon shaded water limits gameplay because you can't have underwater portions because the water is blue, rather than see through.
And no, it's not smart. Using these kinds of graphics makes no use of what the Wii U is capable of clearly leads to lower sales, based on what we've seen.
In no way shape or form is using realistic graphics the cheap route. If anything, it's the other way around seeing how much easier it is to use cell shading.
We had under water sections on Skyward Sword didn't we? And just because you fail to picture that Wind Waker could do the same, It doesn't mean that It doesn't. As I said, realistic is more time consuming and takes more disc space, that will directly impact the game length, gimmicks, engine, etc.
Why do you think non realistic graphics = lower sales? You're wrong.
NOBODY, BUY ZELDA GAMES FOR GRAPHICS. Shooter (few exceptions, such as Gran Turismo 5) tend to have the "best" graphics, you know why? It's because graphics in that case is a huge part of the experience due to It requireing to be realistic. Shooters copy the real world, they NEED to be realistic. Zelda on the other hand? It's a waste. Seriously, It's waste of money, development time, disc space and everything. Nobody buys Zelda game for graphics, ZELDA DOESN'T NEED TO BE REALISTIC. You have to face the fact that there isn't much to improve graphic wise from PS3 and 360, actually, Wii U is uncapable of doing that. PC will always be better and always have a superior version graphics wise and those who want graphics tend to use that instead. But what Wii U can do is make an upgraded Skyward Sword graphics and I can guarantee you, It will be highly praised, even more than realistic, which wouldn't show us anything groundbreaking. There is a lot of room to improve and they're quite obvious to those who know anything about graphics. Textures, lightning effects, 3D model bones, polygon count, anti aliasing, etc. Nintendo could make Skyward Sword graphics better by a huge margin while still mantaining It's colorful/cartoonish/anime look and show Wii U potential that way. You have to remember console games can't run on Full HD without major frame drops, they run at 30fps instead of 60fps, that's why we don't have even beatiful games such as Uncharted 3 run on 1080p. While Wii U most likely would be able to do that, non realistic graphics still would have smoother animation with a more stable fps.
Cel shading (btw, Skyward Sword =/= Cel Shade) isn't easier to develop than realistic, less time consuming is the right word. With realistic graphics you can use real world texture and base yourself on real humans, that can't be done on cartoonish graphics. You have to create everything from a scratch. The only reason It doesn't take longer is because you end up using less polygons on the 3D models and simplified textures. Cheap tactics are the ones that people tend to highly praise for pretty much no reason, like how CoD and BF always come back with a slightly updated graphic and pretty much the same gameplay and people treat It like It's groundbreaking. Making a game that works perfectly with cartoonish graphics go realistic is an attempt of doing that, or maybe making a slow paced game faster paces with a few of those famous shooter elements, kinda of what happened to the Resident Evil series. In general, those cheap tactics tend to disapoint older fans and are clearly just there to milk the series without giving a damn about how good It is.