Because most of the games were made for the consoles, and then ported and "enhanced" for the PC.

For the same reason a PC with 6GB of RAM can play the same games with just as much graphical detail as a PC with 32GB of RAM. Most games do not use a ton of RAM. 7GB actually seems like overkill. Even games like BF3 on PC don't use more than 4-6GB of RAM.

I am figuring that, the first few years, you still have gaames in the pipeline which can also work on the 360/PS3 and next gen consoles, that should be able to fit on the Wii U once they start maxing out the memory.  If they don't design a game to scale down RAM usage, but maximize it, then are people still say EVERY single videogame made in the future, is going to be able to be scaled down?  And here I am not talking about stuff like Black Ops: Declassified, which is its own spin off, but the same game.

Won't be a huge issue until later in the ps4's life cycle, just by lowering the textures, shadowing etc. They should be able to fit the same game into the wiiU version. They could even make it 720p instead of 1080p. But keep in mind that currently 8gb's is way overkill, they will only need maybe 4gb's for the first few years.

The target system the games were coded towards is the PS3 and 360.  Idea was that scaling up was an option.  Next generation, more and more third party are going to target higher end PCs and also the PS4 and next Microsoft console.  When you do this it is an entirely different animal.  On that note, here is a question: If you were attempt to adopt Skyrim to the Wii, what would it be like?

Same way PS360 "fit" games that on the PC required 2GB to 4GB of RAM.

Its called scaling and optimization to the hardware.

To put simply, yes it is possible for a game like Skyrim to run on the Wii, will it ever happen? Not a chance.

Skyrim uses a *very* similar game engine to that of Oblivion right down to how allot of the graphics pipeline works, it certainly wasn't the technical leap that Oblivion was over Morrowind for instance.

Now what modders did with Oblivion was dumb down the shaders, reduce the textures, reduce the geometry, reduce the draw distrance, reduce the lighting, reduce the shadows and scale down Oblivion to run on PC hardware that was about equivalent of the origional Xbox, but with a GPU slower than the origional Xbox. I.E. A Geforce 3 and not a Geforce 4, the Wii has more processing capability than that.
However... The game would simply look horrible and framerates less than ideal, but the PC also runs a full blown Operating system with other applications and services in the background.

Also the reverse can happen too, Skyrim for instance because it was technically and graphically a pretty horrible looking game by PC comparisons thanks to Bethesda having the consoles as the lead platform... Modders took it upon themselves to improve it. - And improve it they did, it can look stupidly stunning, better than any console game ever released, the same goes for Oblivion and Morrowind too.

Pretty much this, i dont know what magically version that some people are playing on WIi, but those games generally ran like crap on Wii. And thats even more troubling considering that COD games have never really pushed either ps360 hardware much, what about stuff like Crysis. What i think is going to happen is quite simple, the WIi u might just miss out on a lot of games just like the Wii did before it.

World at War and Modern Warfare 3 on Wii ran pretty well, actually. They weren't silky smooth, but they were playable just fine.

And most PS4 games won't push its hardware either. 

I'm not sure what you mean by "(if not even less)" as Nintendo made that full 1GB available to developers and that wont change.  If it was to change at all, Nintendo would most likely open up some of the 2nd GB once they have their OS optimized and are pretty sure they would never need the extra space (after building in an extra buffer to begin with).

As for your question about a game built for 7GB being used on a system with 1GB.  First, your going to find that extremely few games during the life of the PS4 will have to use all 7GB of memory.  The ones that do would be more difficult, but not impossible to port to the Wii U.  A couple of sacrifices that would be made is less of the game in memory so there would be a more frequent need to load and the second thing I would image is lower quality textures.

Sony themselves have stated that not all games are going to be huge productions which is going to be true because the developers just don't have the resources to give every game a $100mil budget.  I would guess that 90% of the PS4 games released would be fairly easily ported to the Wii U .  I believe that most of the rest could be, but with a hit to the overall quality.

I'm finding that both of my sons and their friends seem to be into the more retro indie games lately, if that trend was to continue, all three 8th gen systems would have no problems.