That article covers the history of chips (CPU and GPU devices) that Apple has historically used, from their Motorola roots, to the PowerPC, and then to Intel for computers (Mac and MacBook systems) and ARM for their mobile devices (iPhone, iPod).
(Note: "ARM" is technically named ARM Holdings, and is headquartered in Cambridge, England, UK.)
The A4, ARM, and Nvidia Tegra
I haven't been able to find any tech specs on the Apple A4 processor yet, but according to this ARM Wikipedia page, the original Apple iPhone came from the ARM11 family, and the iPhone 3GS comes from the Cortex family, with the ARMv7-A architecture, and Cortex-A8 core.
From what I've read, the A4 is most like the Nvidia Tegra, another SoC ("system on a chip") device. As that Wikipedia pages states, each Tegra chip is a nearly-complete computer on a chip:
Each Tegra is a "computer on a chip" which integrates the ARM architecture processor CPU, GPU, northbridge, southbridge and memory controller onto a single package.
Time will tell if the Apple A4 processor/chip is better than the latest Nvidia Tegra design, where the word "better" means some combination of performance and power consumption. (If the A4 is both faster and uses less power than the Tegra, it is clearly "better", but if it doesn't meet both of these standards, the word better will probably just imply a compromise.)
Rationale for Apple's A4 chip
As a final note, even if the chip isn't better, I can certainly understand Apple's rationale for having chip design done in-house. When I owned a software development company, we very quickly found out that we needed to employ not only programmers but also designers. We had several really bad experiences in trying to outsource design work, and quickly decided we needed people in house we could work with. At that time -- over 10 years ago now -- that was almost unheard of, but it was something we knew we needed, and we flourished because of that decision.