Agreed. I don't think Apple will crack down on the little guys and little sites hacking OS X to run on non-Apple hardware; the more people use a sort-of, kind-of Mac, the more interested they're likely to become in a no-compromises version. At least that's true of hobbyists who go in with both eyes open and know that they're applying a kludge and can expect no support.
Folks buying a turnkey Mac "clone," on the other hand, are more likely to think that it's actually a Mac, and when it isn't stable or upgradeable, more likely to be turned off by the Mac altogether.
All that aside, I know that in some areas of intellectual property, you can lose your IP rights if you don't make a good faith effort to enforce them. I don't know if the courts have ever applied that to a EULA, but it's possible that failing to enforce it here would be a first step to it being considered unenforceable later.
You have some very good questions and observations. Apple will get blamed for any of the problems of the clones. Microsoft got blamed for poorly-written programs that had problems on Windows, and Windows is full of application-specific hacks as a result. Clones would be very bad for Apple's image.
But as far as the EULA goes, I would like to see that contested and rendered unenforceable in part. Too many EULAs today do their best to strip you of your consumer and even constiutional rights. Many say you can't publish benchmarks or product reviews without consent, which of course means poor scores won't get published and the public will be less informed. Both Microsoft and Network Associates have tried to enforce these. The NA EULA for McAfee was deemed unenforceable after NA used it to silence some unfavorable reviews.
Microsoft backed down rather than have a EULA found unenforceable after some very poor benchmark results (not a hack job, MS reps actually worked with them to try to get better results). Microsoft EULAs don't prevent publication anymore, but they do enforce some rules. I think the rules are reasonable, but it's still an infringement on free speech. They can sue for interference with trade or defanation if unfair benchmarks are published.