That is not law. There is nothing criminal in running Mac OS X on a PC.
Sadly, in the United States, violating a license, therefore a contract, is punishable by law. It is
illegal. It is not
criminal, though. (Meaning the government itself can't fine you or throw you in jail, but the person or organization that has been slighted can sue you.) It is still
illegal though, in that it is violation laws that cover legal contracts.
In addition, Apple has thrown little things into OS X that also make it a copyright violation to install OS X onto generic PC hardware. This copyright violation
is a criminal violation, thanks to the wonderful DMCA, punishable by government fines, jail time, *AND* direct restitution to the copyright holder.
In short:
Violating a license = contract violation = lawsuit and restitution to contract holder.
Violating copyright = government fine, jail time, and restitution to copyright holder.
Installing OS X on generic PC hardware = both license violation and copyright violation.