I don't think this is true for Japan, and I doubt this will be true for the rest of the world once the big hitters are being launched.
The WiiU did much better than expected numbers during the past Christmas (yeah, I remember that doing better than the equivalent Christmas for the GC on Japan became suddenly expected after the console sold 100K+ in one week) and Nintendo franchises are stronger now than they ever were back on the GC.
The console is selling low because it's catalogue is basically niche titles + platformers. It lacks diversification with big names of other genres, and that problem will be solved this year from the release of MK8 onwards.
When I didn't know MK8 would launch at May 30 and expected it to launch around March I made the claim that WiiU would never go lower than 5000K a week. With MK launching so late it could be possible for it to fall beyond that number, but I sincerely don't think this will happen once the games are released.
Nintendo is clearly betting it all on that second year of the console. I expect them, like they on the past year, to start releasing games at a pace of 1 title per month. It's just that this time they will start on May instead of July and they will have much bigger names of more varied genres to fill the gaps.
Mario Kart on May, Bayonetta 2 / Hyrule Warriors during summer/september, Smash Bros on October/November and X on december. If they could also release games such as FExSMT and another HD Remake like Wind Waker before the end of the year, coupled with the few 3rd party titles that are still released for the console like Project Cars (racing simulators have a market in Japan), I could see the WiiU selling much better than the GC, and even than the PS4 this year.
