They aren't. The console's
library is defined by the games, but not the console itself. The Wii U is a vastly outdated system (within the system of 'video game consoles'; we're excluding gaming PCs here) as it is truly on par with the PS3 as far as, well, everything is concerned. Same disc space (25GB for the U optical disc; 25GB for a single layer blu ray disc, as I recall). Lower memory capacity on the U side (like 3.7GB and around 27.7GB as I recall, Basic and Deluxe models respectively) compared to the PS3 side (20GB, 60GB, 80GB, 120GB, 250GB, 500GB models all exist).[initially; U can be expanded to, what, 4TB using external harddrives?] Clock speeds? I'm not tech expert, but check this out:
Wii U slower than PS3 and 360 | playstation-techzone.com yeah, Wii U is slower than PS3 *and* Xbox 360. I could go on with this, but the point is, the console and the library are two distinct things.
The PS4 automatically is a better console. I don't think there will need to be a comparison of specs, because the Wii U is simply out of the PS4's league specswise. What sells the consoles is the library; as of now we can't concretely say much about either system's library, except that the U is clearly doing poorly as of now.