I'm guessing there's going to be some sort of change in this gen. All of the systems so far have been, in succession, very linear in terms of features and innovation. More polygon counts, graphical prowess, in short, a more powerful machine. This generation, however, the three major companies seem to have something different going for each console they have developed.
The most obvious would be the Nintendo Wii. It is a very different move and approach from the traditional "The newer the stronger" theory. It has been said to death, however, no matter how much you may disagree, the wii remote is new. The function of pointing and motion sensing in a controller hasn't been done in the past. The raw power this console lacks is purely intentional. It is to be cheap, easy to play, and aruguably fun. Nintendo wants to have this image, because it is targeting a whole new market. One that is much broader than the previous consoles. Some of the 'hardcore' gamers may mistakingly state that because the wii is such a simple system, it is a system made for children, however this doesn't seem to be the case. Adults and children alike are appreciating the wii. In fact, older folks, (Older even than these 'hardcore' gamers) are enjoying the system. This justifies the plentiful party themed games that are being released. Children with their simple minds, Adults with their stressful jobs and life, Older people who are just too tired to invest time an energy to a massive interactive story with amazing graphics, (Who, by the way, still will undoubtedly say that the picture still looks 'unrealistic,') that comes with, say an fps or RPG, want games that will excite them quickly, and will be easy to pick up and play without making them think too much. Because this strategy will target a whole new audience, I believe that the nintendo wii will sell well no matter how well Sony and Microsoft will do. (Hold on before you say I'm a total nintendo fanboy, I'm not done.)The nintendo Multiplayer strategy is also drastically different. Rather than playing against people online all the time, the Nintendo Wii indirectly encourages people to play multiplayer games with people physically beside them, which seems to add to the experience.
The PS3 and Xbox 360, target a different market from the wii, but share a similar target with each other. The gamers who desire full immersive stories with breathtaking graphics will find it in the PS3 and the Xbox 360. These two consoles target the gamers who have time to sit down and play. With new rising technology such as HD disks (HD-DVD and bluray), progressive scanning with higher resolutions, the two consoles really emphasize the power that they hold respectively. Since the hardcore gaming audience has somewhat changed over the course of the last few consoles, game companies have been targeting that audience only. It isn't to say that since the wii has targeted a broader audience, it will do better, since the hardcore consoles we have had in the past such as the ps2 have done so well.
All in all, even if it seems that I support the wii more, I believe the wii will do well. Because of the giant differences between the wii and the PS3 or Xbox 360, I wouldn't be surprised if households owned both a wii and a PS3/Xbox360.