AppleInsider has a post up about a potential interest Apple has in ARM Holdings, designers of the ARM processor cores used in the iPod, iPhone, and iPad, among tens of thousands of other devices. Apple has a market cap, of almost $250 billion, while ARM is just shy of $2 billion. Apple clearly has the cash abilty to purchase ARM outright, and they certainly have a reason to want to.
However, the rest of the computer world has an even bigger reason to keep Apple from doing so. ARM devices are used by tens of thousands of devices, made by thousands of companies. Silicon containing ARM IP is made by hundreds of companies across the world. The success of these companies, their designs, and the devices they power is in large part based on fair, equal, and predictable availability of licenses from ARM.
If Apple were to own ARM, they could completely stop the availability of licenses to any design they felt was a competitor, or they could delay the release to third parties of newer designs. This is similar to the problem some phone companies are experiencing with Google and their Android OS, Google is motivated to sell their own branded Nexus One phone, with the latest version of Android, before giving the same version to third parties.