Don't count on it. The problem with virtualization is that it requires the virtualized OS to be as cooperative to the whole affair as possible, since it needs to be fooled into thinking it has unfettered access to the system, which in many ways is much harder than just getting the OS to run natively on the hardware. Windows and Linux are becoming more virtualization-friendly every day since their developers have realized that their operating systems are being virtualized on a regular basis, but since there is no Apple-approved way to virtualize OS X, it would be a fairly trivial matter for them to make it as unfriendly to virtualize as possible. If that doesn't sound like such a big deal, consider how many strange bugs there are in VMs where the virtualized operating system is TRYING to make it as easier on the VM.
Is Apple doing this at the moment? Probably not. Would they if they saw OS X virtualization becoming widespread against their will? Of course no one can say for sure, but I don't think anyone would put it past them either.