I can understand why they chose to ride with the name Wii U, they worked hard to establish the "Wii" brand and were very successful at it. The success of the product is the key...this is why we don't see "super" versions of Saturn or the Pinto, for example.
"Wii", though a couple years out of its hey-day, commands instant recognition and (Nintendo is banking) elicits positive feelings within target consumers. It is their play at the expanded audience that they hope to recapture, the customers they MUST convince as they already know their relatively small core audience will purchase regardless of the branding and they know the non-faithful core will not be their lifeline with two firmly entrenched competitors soaking up that market segment.
Additionally, the derivation is logical along the lines that the Super NES followed its 8-bit brother. The Wii U especially, while being a separate console, exists very much in the same vein as its predecessor, right down to compatibility with all of the original Wii's games and peripherals. This is another strong selling point and another good reason to tie the new console's branding closely.
As to why the console itself looks so damn alike...ugh, ya got me there. Oh man, Right down to the same colour and practically the same shape and size... maybe their market research concluded that small, white and boring is what Apple would do? I dunno. (I advocate black, myself, especially if they really want it to "blend into" the rest of the living room rig.)