The experience provided by handheld and home consoles are similar enough as to warrent comparisons; that is the point. And, by gaming, I'm being a little more specific than saying they both entertain. The sales of both are driven by very similar means. For instance, if some mega-selling software came out on the 3DS, it could bolster the handheld's sales in general. So could it be for the Wii U. Moreover, that which caused the 3DS's sales uplift (pricing, modeling, software, or whatever else happened) might be done to the Wii U. That's pretty much what happened with the PS3, anyways.
In what way?!?! The consoles have local multiplay, better graphics, can play media like DVD, bluray etc and of course, can be put onto a 42"+ TV.
A handheld does none of that.
If a new fiesta comes out with new features, it will sell, just as if a new BMW 5 series comes out with new features. You are comparing a micra to an Aston Martin, and farmville to CoD. Stop it; it's absurd.