I work distribution for the guys who stock Tesco (Oakwood), a lot of the smaller Extra stores aren't able to implement the shelf space because they don't have it. It's largely down to store manager discretion and a lot of the merchandisers i know are having to put up with a lot of crap from reps over it. I've mentioned it previously but Nintendo are the worst for hassling merchandisers, who are only there to tick boxes and do things in their best judgement, they don't make decisions for stores. Them and Paramount people are like dealing with monsters who don't understand the word no.
I wouldn't mind either but other than the launch, we aren't asked about the Wii U as much as any other hardware. People really don't care.
The picture Chopper posted is very typical in all though, the majority of managers i've worked with have dedicated 3-5 times more shelf space to both Xbox and PlayStation and even give equal measures to Skylander and now Disney Infinity. With the exception of the 3DS, Nintendo stuff is at the bottom of the totem pole alongside PC games (with the exception then of Football Manager, The Sims and the occasional World Of Warcraft expansions) but then again since i've been doing the job, the software sales rate hasn't been amazingly high anyway.
From a retail point of view, the Wii U is a damp squib.