Let's look at the small victory for Psystar first. After Apple filed its original suit against Psystar, the clone maker decided to counter-suit, claiming Apple had broken antitrust law. This counter-suit was dismissed by Alsup, but today he did allow Psystar to modify its case against Apple, shifting the focus from antitrust to Apple stretching abusing copyright law instead. "Psystar may well have a legitimate interest in establishing misuse [of copyright] independent of Apple's claims against it," Alsup argued in the ruling, "for example, to clarify the risks it confronts by marketing the products at issue in this case or others it may wish to develop."
The more interesting note is the hint Alsup made at what would happen if PsyStar were to win this case via the misuse of copyright route. "Moreover, if established, misuse would bar enforcement (for the period of misuse) not only as to defendants who are actually party to the challenged license but also as to potential defendants not themselves injured by the misuse who may have similar interests." That's crazy fancy schmancy legal talk that means something along the lines of this: if Psystar wins, other companies would be allowed to sell machines with Mac OS X pre-installed as well.
With this clear hint, it becomes quite clear why Apple is keen on winning this case. If this would indeed set a legal precedent, allowing everyone to start re-selling Mac OS X, Apple will face a world of competition. Possible solutions for Apple would be to make the retail copy of Mac OS X really expensive, or to include a copy protection scheme that falls within the DMCA. Still, such a scheme would mean very little outside of the US, where the DMCA obviously doesn't count.
Personally, I find it a little odd that Apple and its fans are so afraid of what would happen if Psystar were to win and other companies would start selling computers with Mac OS X as well. Apple fans always claim that Apple's hardware is competitively priced and of higher quality than similar machines from competitors, so what is there to fear? Surely, people will still buy Apple's machines in favour of the clones, seeing the Apple machines are so much better and more value for the buck?
Yes, you're right, there is a lot of sarcasm in there. The reason for that is that we all know that cheap and unambiguously legal clones could mean a massive loss of hardware income for Apple. It has happened before, and it could happen again.