Why does Windows 8 Hyper-V require SLAT?

Since Windows 8 is designed as a desktop/workstation or client OS, the requirement for SLAT makes a lot of sense for most users.

The lack of SLAT (Intel EPT and AMD RVI) was a big issue when using Hyper-V and a Windows 2008 (r1 and r2) system equipped with a high-end video card as a workstation (as opposed to a server).  When 2008r2 became able to use SLAT, the video performance issues were just resolved.

VPC Guy Ben A has an excellent selection of blog posts on SLAT and Hyper-V.

Issue: Video performance may decrease when a Windows Server 2008 or Windows Server 2008 R2 based computer has the Hyper-V role enabled and an accelerated display adapter installed

http://support.microsoft.com/kb/961661?wa=wsignin1.0

Expanded explanation of why it happens:

http://blogs.msdn.com/b/virtual_pc_guy/archive/2009/11/16/understanding-high-end-video-performance-issues-with-hyper-v.aspx

SLAT resolution:

http://blogs.msdn.com/b/virtual_pc_guy/archive/2011/01/17/using-hyper-v-for-a-high-end-desktop-computer.aspx?Redirected=true