One thing to consider is that the Wii and the Nintendo DS are the cause of a lot of unprecidented growth in the industry; this is partially caused because they appeal to new gamers who are not likely to become interested in a PS3 or XBox 360 regardless of the price, and also caused because of how unique they are in the market place encourages growth in multiplatform ownership.
On top of this the XBox 360 and PS3's main selling features are technological and feature improvements which (for the most part) the mainstream audience is not ready for, and will not be ready for until the next generation; HD is wonderful, but with the slow adoption rate and the potential slow down in the world economy it will not be a key feature until 2011 or later; at the same time, online gameplay is also a great feature but we are still years (or decades) away from most gamers playing multiplayer games online.
The combination of these factors, along with the enevitable boost that the dominat console gets from the additional support it earns, means that it is unlikely that the PS3 or XBox 360 will ever approach the numbers of the Wii, and it is unlikely that they will be able to capture 40% to 50% of the marketshare combined. This (of course) is not a death sentence because of the unprecidented growth I mentioned earlier; it is likely that there will be 220 Million (or more) consoles sold this generation, and at 40% this would mean that Sony and Microsoft would have 88 Million consoles sold between the XBox 360 and PS3.
