Having played it at E3, I do expect Wii U to start less strongly on the market than Wii did, simply because its probably going to take some time to explain the controller functionality and for interesting gameplay to show up, whereas with Wii the controller / new game play ideas were immediate. On the other hand, EA, Ubisoft, Activision, THQ do seem to be preparing big games for launch, and these days those companies are much more important than the Japanese publishers that supported the 3DS launch. Good Western support, a couple games from Nintendo, and the flood of enhanced ports with the Wii-name should assure a decent launch in the West.
Its also worth noting, as a point of comparison that the lines for the 3DS at E3 2010 went 4 hours, 2 hours, 20 minutes from day one to three, whereas for Wii U it was more like 4 hours, 3 hours, 3 hours over day one to three - and the 3DS had several more 'actual' games to play than Wii U.
The other element of all of this is of course is that during the March 2013 year Nintendo (especially with a price cut) can still ship 7-11m units of the original Wii in addition to the Wii U. Even at 9.5m in that fiscal year, Nintendo would ship more Wiis than it did N64s or GCs in their best years, and 9.5m would still be close to the SNES peak as well. The Wii U doesn't have to explode immediately - 5m in the March 2013 year along with 10m Wiis would be flat on the March 2011 year (15m Wiis) by units and by revenue, and up on the March 2012 year (13m Wiis projected). The real trick will be the March 2014 year, when Nintendo is completely out of tricks to keep Wii up (price cuts won't work, virtually no new game releases, new consoles, etc) - Wii U has to be performing well by then.
