There are dual layered, and Tripple Layered discs, so if a single layer on a disc is 25GB in size, and there are 3 layers it will have 75GB=25GBx3 layers. Most likely the disc drive in the Wii U can at least play Dual layer disc since most disc drives for PC and laptop are now dual layer, and I think most dual layer disc drives can play tripple layer discs since there are only dual layer drives, and no tripple layer drives you can buy for PC.
I think most Wii U game disc still won't fully fill the 25GB since Age of Conan: Unchained which is a
massive multiplayer online game for PC/Steam download size is 18.90GB . Plus, making massive games with hundreds to thousands of hours of gameplay would be very expensive if the game has a lot of original levels with different plots, characters, and enemies, and many people dislike filler and grinding levels which aren't really fun to play, and just want to get quickly to the boss fights.
Nuke, could mean the video card RAM being 1GB of dedicated RAM unlike the PS4 and Xbox 1 which uses an APU which combines the CPU with video card, chip, and shares the RAM and CPU with each other like integrated video.
The AMD APU series of chips are originally made for cheaper netbooks/ultrabooks, and low end desktops for people who don't want to buy a expensiver desktop with a seperate video card, and high end CPU like the Intel i5-i7 quad core CPUs and a Nvidia Geforce GTX 650, but want slightly better video performance than an Intel HD4000 integrated video chip.
The Wii U also has expensive, but faster eDRAM on both the CPU and video card chip. eDRAM is a lot faster than regular RAM since it is located on the chip for better performance because the chip can access eDRAM memory a lot faster on the chip than regular DDR RAM memory on a stick or chip outside of the chip.
"
embedded DRAM", a
capacitor-based
dynamic random-access memory integrated on the same
die as an
ASIC or
processor. The cost-per-bit is higher than for stand-alone DRAM chips but in many applications the performance advantages of placing the eDRAM on the same chip as the processor outweighs the cost disadvantage compared with external memory.
http://en.wikipedia.org/wiki/EDRAM