Retail copies of Mac OS X are essentially upgrade copies, they're only licensed to run on Apple hardware and all Apple hardware ships with OS X pre-installed. This would be roughly the same as a computer manufacturer installing upgrade versions of Windows Vista on a computer. Now whether those provisions in an EULA are enforceable is a different question, it looks like they probably are though.
I don't think this is an issue of first sale either as Psystar is not merely reselling a purchased copy of OS X, but installing it in violation of the EULA. Maybe if they shipped the computer without an OS and shipped a boxed copy of OS X you could make a first sale argument.
More importantly with regards to Psystar, they're hosting and distributing modified versions of Mac OS X updates. This very clearly is a violation of Apple's copyright on those updates. Best case for Psystar in this is Apple gets an injunction preventing Psystar from hosting updates. Psystar can still sell computers with OS X, but customers are completely on their own in terms of updating. Not good for anyone really.