[citation][nom]iamtheking123[/nom]Errr, no. A material only has one rating...thermal conductivity (there's no holding vs transferring). It's either good at transferring thermal energy or it isn't. Copper is the best, unless you want to pay for silver, and aluminum is a bit more than half as good as copper. (Fun fact, gold is worse than copper but better than aluminum at heat transfer). Heatsink manufacturers can "cheat" though to save cost and use copper bases with aluminum fins, because at the point of the fins you have a lot of surface area and it's the air that's the limiting factor of heat transfer. However, you also get a minor choke point at the copper base -> aluminum fin interface. Thus, an all copper heatsink is best if you can afford it.[/citation]
This is correct, but I would like to add that copper weighs more than aluminum. Even the most expensive heat sinks are likely to use aluminum fins in order to cut down on the weight.
On a desktop motherboard, heavy components put strain on the PCB, and in a laptop you would have to lug all the extra weight around. Using a selection of different metals is just good design.
As for the article, my experience with Macbook Pros is that they run dangerously hot. Forcing Macbook Pro hardware into a Macbook Air-style body is only going to make matters worse unless they make serious compromises in the performance of the hardware, which would weaken the Pro's position as a high-end laptop.
It's a moot point as far as I'm concerned, though. Any laptop Apple releases is going to be too expensive for what it does.