Apple has a different perspective
Apple introduced new PowerMacs today. At the high end are new dual 2.3GHz and dual 2.7GHz G5 models. Many people are already complaining about the "just 200MHz" speed bump for the high end model and the choice of ATI Radeon 9600 and 9650 as the base graphics cards.
This PowerMac revision is obviously not a major upgrade and Apple treated it as such. Apple's home page, is mostly full of Tiger stuff and the new PowerMac intro is just a small image on the lower left corner.
A clock speed increase of 8% for the top model may not be that much of a speed bump, but neither Intel or AMD has been able to pull off dramatic clock frequency jumps lately. Clock speed stagnation seem to be a general problem in the processor design industry.
As for the dual cores, obviously AMD and Intel have much more incentive. The entire PC world is built around a standard form factors: ATX motherboards and ATX cases. Intel's efforts to move to a new form factor (BTX) has been quite unsuccessful so far. It is very hard to put two "hot" processors on an ATX motherboard in an ATX case. PC market is also driven by cut throat price pressure and low margins. There is a huge price difference between the prices of single processor motherboards and dual processor motherboards. Given the stagnation in the clock frequency, the only practical way for Intel and AMD to drive the mainstream PC to higher performance is the SMP model through dual-core chips. This way, all of the rest of the system components (motherboard, chipset, case, cooling system) can stay the same.
Apple does not have this constraint. Apple has been manufacturing mainstream multiprocessor desktops for manty years. Overall, it may actually be more cost effective for Apple to ship multiprocessor system. It may be a lot cheaper for IBM to manufacture two instances of a small die like the PPC970 FX (less than 60mm2) than a larger dual core die. As for Apple, having the source of the heat distributed accross two chips makes thermal management somewhat easier than dealing with one extremely hot dual core chip.
I am sure Apple will eventually move to dual core PPC970MP chips, potentially later this year, but this will most likely be in the context of being able to offer quad systems (two dual-core processors) for higher performance.
As for the choice of the base graphics card, the 9600 or 9650 is a perfectly reasonable choice. The primary driving force behind high end graphics cards in the PC world are 3D games. PowerMac G5 is obviously not the best 3D game platform. Most people buy PowerMacs to use in professional applications. Many pro applications do not require super-duper 3D performance. For those who are planning to do serious 3D work, the 6800 Ultra upgrade is the reasonable choice. There is no reason to burden all customers with an expensive (and potentially loud) graphics card.