But the game is the production stage, that's where the sounds are mixed, reverberation and other effects are added and projected over 5.1 or 7.1 channels. To get the best results you need lossless compressed audio, preferably in 24bit 96khz to give you enough headroom to do all the calculations. You can downsample it after all the mixing is done and all effects are added. However outputting it in 24bit 96khz is still preferable if your amp is going to apply extra filters and effects as well.
For textures compression doesn't matter as much as resolution. If the WiiU is going to do 1080p then you better get some higher res versions of textures for up close, requiring a lot more space.
25gb should be enough without too much pre rendered fmv. The Witcher 2, although not so high quality in the sound department, has pretty good texture detail for 1080p and is about 15gb. But if you add tons of high quality pre-rendered fmv in 2D and 3D versions then a 12gb game quickly turns into 41gb, see Killzone 3.
Anyway the chances that 3rd party devs are going to do HD sound mixing and make higher res textures for WiiU ports is pretty much 0. Nor do I think Nintendo will do it themselves. Stylized graphics is their strong point, not detail, same for sound effects. But it's nice to have 25gb available for ps4 / nextbox ports.
Keep in mind that the Blu-ray drive in the PS3 is slow (only 2x) and developers have used redundant data for most games as a way to reduce seek times and disc spins. If the optical drive in Wii U is faster (and I see no reason why it won't be as even the cheapest of the cheap BD drives are 4x with most being 8-12x now with still 18 months to go) then the volume of redundant data will be reduced greatly - likely to no redundancy needed at all.
Witcher 2 is also coming to the X360 now. We'll see how much of an impact the lower capacity has on the graphics, content and audio and how the faster drive speed of the X360 reduces redundant data.
[PS3 - 9 MB/s || X360 - 16.2 MB/s]
The rEVOLution is not being televised