Because they aren't running everyting in the emulator - the kernel, drivers, many of their own apps, and in future possibly 3rd party apps as well are run nativ

Because they aren't running everyting in the emulator - the kernel, drivers, many of their own apps, and in future possibly 3rd party apps as well are run natively. They're emulating x86 for apps and some system DLLs. (There's a schematic at about 8 minutes.)