The problem with the Wii U sales isn't something that simple. But its close. The main reason is the economy and the "free market". People will only pay as much as the market can bear, and right now with the conditions that are currently going on in the US and Europe buying a new system that has a over $300 price tag isn't something they can just go out and do. And with the problems that the sequester program cuts are going to cause their ability to buy luxury impulse items such as game systems is just going to diminish.
And when it comes down to whether they will buy the new Smart phone/iPad or a new game system, the Smart phone will probably win. Because luxury items are usually meant to show off, and it is easier to show off a phone you have with you and not a system. (Because that is just the way the mass market works.)
So it isn't just the Wii and Nintendo handling of the Wii's software, it is also the 360 and the PS3. Because most who are looking to get a game system who are not consider a system's "core" base, or those who will buy the new system no matter what, they will look at the new system and see an expensive system with a few expensive games, usually sitting next to the older cheaper system, with a ton of games ranging from a few dollars to $60, and some of those games make up a good percentage of the new system's library. Now what you you get go out $600 and only get a system, and at most 3 or four games. Or spend $400 and get a system and the same, or in their mind comparable, games. (Because in most non-core gamers mind there isn't that much of a difference in squeals, so they will prefer to pick up the Killzone compilation in favor for the lure of a new Killzone on the PS4)
So you can view what is currently happening to the Wii U as a portent was what the market is going to be like for the PS4 and the next Xbox. You will have your cores buying up the system during the first few months on the market and then the sales will go down to a trickle. Because your average customer will not be interested in getting the latest and greatest if there is a cheaper alternative on the shelves, with a bigger library and the "same games" out on the older machine.
Also the case of no backwards compatibility is going to play a difference in the first year of the machines lives, especially if some of the titles are going to be $70 like Patcher is contending. (Even though he isn't correct usually, but even a blind man can get a bulls eye if he throws enough darts.)
As for the core not all will adopt the new machines, Kotaku recently put up the results of a survey which concluded only 29% of those who consider themselves core, probally by how much they play and buy for the machines, will be first adopters. Which is the feeling I get when I go to different boards and see comments like "Very nice machine, I will get it once the price drops to $250." It seems $250-to-$300 is going to be the magical number this generation, because that is the price most are drop some are saying $350, and less are $400 and above. (I consider those are the core who will buy no matter what.)
So I would say after that there is two things Nintendo needs to do, one a price cut, we already see they are doing something like that with the ZombieU bundle, more 1st party games and a bigger library. Then they will go on the upswing, and probably will become a barrier for the new console to get over in 2014.
Source of the 29% - http://kotaku.com/5988269/?post=57954381
