I'm not sure the ability to chat with the hypervisor is the thing that makes the difference. With VMWare you should be able to use rexec or ssh to get back to your basic Linux and tweak things (provided there is a command line interface).
It is very hard to fully virtualize the platform the hypervisor runs on. zSeries virtualization with z/VM goes pretty far in this. That's why you can run z/VM in a virtual machine, and run z/VM in that z/VM, etc. As far as I understand you cannot run VMWare in a Linux system that is running on VMWare.
Still difficult, but easier, is to provide something that is just good enough to run another operating system. When you know which OS to run, you can take shortcuts in the virtualization to make the process less costly. I believe that is why VMWare makes the different types of environments.
When I tried to run my Windows system under VMWare it presented a different environment that caused Windows to load different video and network drivers and caused me a lot of trouble to run native again. I'm certainly not trying that again.
Rob
