Wrong way round...

They should really certify it the other way too - windows guests running on top of a suse linux system running xen or kvm or whatever hypervisor technology suse supports.

This is more useful for many reasons...

Linux can be stripped down much more, leaving you with a lot less scope for security holes or patches that need installing... Aside from that far less linux patches require a reboot - the impact of rebooting a box that hosts multiple virtual images is quite extreme and well worth avoiding if possible, and having to reboot a vm server because of a web browser patch is just insane.

Having a stripped down host also reduces overheads, running a vm hypervisor should not need several gigs of disk space, save it all for your images.

People migrating to linux may find themselves with one or two apps that require windows, running them on a vm until they can be replaced is a common situation. People migrating away from linux often don't have such constraints because most linux apps follow standards and can be easily replaced, or are open source and have been recompiled for other platforms.