What's the fuzz....
Sorry, my fellow Mac fans, but Apple can only sue Real if Real is breaking Apple's Intellectual Property (copyright or patents) or the law (DCMA).
Now, Real will introduce software that is able to produce AAC files containing Real's own DRM. From the outside these files will behave exactly the same as the iPod expects from Apple's iTMS AAC/DRM files. The behaviour of files is not the subject of copyright. If Apple was unable to patent the behaviour of their AAC/DRM files, Real is safe there too.
Real discovered what behaviour the iPod expects from a file by reverse engineering the iPod software. This seems legal, also under DCMA, because they didn't reverse engineer the software in order to break the code of iTMS AAC/DRM files or to promote illegal copying, but to be able to produce their own compatible AAC/DRM files. Reverse engineering for compatibility, even of patented software, is legal because we all like a free and fair market. Real doesn't need to copy or mimic the iPod software itself, so there is no chance on infringement on copyrights or patents there.
So as long as the DRM encoding software of Real doesn't copy code or use patented technology in their software or in the files' behaviour they're perfectly safe and legal. One may assume that Real's lawyers investigated this matter thoroughly (although you may never know if Apple comes up with some "surprise" patent).
Further, it will extremely be difficult for Apple to change their DRM such that Real's files will be rejected by the iPod like they announced, without rejecting already sold iTMS files.
If Apple is not providing serious base for their charges soon they may even be sued for illegally obstructing the free market by falsely discouraging Real's customers to buy, and may be held liable for damages by Real.
This case is a bit similar to a case that arose here in Europe last couple of years about the "Senseo" home coffee brewer and its coffee pads (sort of disc shaped tea bags, but filled with coffee). The brewer was patented by a well known coffee producer (Sarah Lee/DE) in cooperation with Philips, but it turned out that the coffee pads that it uses could not be patented because coffee pads as such were already known (although never succesful for lack of a proper brewer). So once that was clear all other coffee producers started to sell (much cheaper) coffee pads for the brewer, which was found legal by the courts (at least in most countries; in some countries it is still not sorted out). Of course the patent owner was pissed of by this, because he expected to have a monopoly, and make a lot of money on the coffee pads, and therefore had sold millions of brewers very cheaply, even given them away in promotional actions. Wrong bet.....

Apple's strategy is much better, by selling expensive hard drives (iPods) and cheap songs....

Heck, they shouldn't care who sells the songs....