That's really what it is. 32-bit Windows applications on 64-bit Windows are running in what is essentially an emulation layer. It's a fairly thin layer now, but remember that the original 64-bit Windows ran on Itanium. The original Itanium had an embedded (slow) x86 chip for compatibility. I'm not sure if WoW ever used it, but certainly the WoW for Itanium 2 didn't, since it was dropped for that processor.