I believe the response is (also as a non-hacker) that KVM is operated in a couple key situation that would either make that impossible or highly difficult. Elaborating, the data center is where most virtualization is being done, though it's moving into the local server cabinet. As a result you run into a couple situations, the first is that the people maintaining the server and the host have no data access to the guests for security reasons.
The second is that accessing the guest to run perf won't provide the complete picture and could mislead you. You really need perf on the host to see how the guest is interacting with the host and other guests. IIRC Vmware provides tools which allow this kind of performance analysis with their Sphere products and they don't require access to the hosts to do it.