According to Rafael Rivera, one of the authors of Windows 8 Secrets, there is a work around that involves creating a shortcut to the desktop and scheduling it to run at boot. But, it appears that even enterprise customers will be blocked from making the standard desktop the default environment. While Redmond is no doubt implementing such a policy to enforce consistency, it could prove to be a source of frustration for big businesses, which are notoriously resistant to change.
Of course this is all fluff to to speak, so everyone will have to wait and see how Windows 8 turns out when it is finally released.
