Chalnoth said:
Two answers.
The first is - so what?! People are buying notebooks with desktop P4s in them. They are big, heavy, and have a horrible whine from the small highspeed fans. But they still sell quite well because people like the idea of a powerful computer they can take anywhere, and which doesn't require any dedicated space in their homes. Plus of course, they sell to the people who always bite on the bigger numbers. A 16-pipe part on a tweaked process geared towards mobile use, fits nicely into this part of the market.
The second answer is power management. Dynamically change voltages and frequencies of the chip depending on both usage and if battery powered. This can't perform miracles unfortunately. The cooling system must still be designed to cope with the worst case in terms of size and weight. Fan speeds can be adjusted though. Also, while there are tricks that can be utilized dynamically managing power modes within the same chip, these should be of fairly limited use for a 3D gfx ASIC, the whole point of which is that it actually ran reach very high levels of utilization when performing its specific task. Nevertheless, there may be some low-hanging fruit that hasn't needed to be taken advantage of yet that might be useful for a part such as this. (So far I've only heard of the entire 3D core being put to sleep when only 2D is used.)
Overall, it may well be possible. I would never buy such a notebook myself though. I like portables to be light and since you typically have it right in front of you as you use it, quiet. Priorities differ however.