in the comments:
What happens to Xen now? What happens to the Red Hat investment on it?
The official press announcement don't say it explicitly but the choice of words lets clearly understand that Xen is the past and KVM is the future.
It's unknown if Red Hat will continue to support Xen or what will happen to those enterprise customers that adopted RHEL 5 to use the hypervisor (mostly because Xen and KVM virtual machines are incompatible).
In any case it's unlikely that Red Hat will drop Xen tomorrow: the company sits in the Xen advisory board and its support policy implies that any distribution must be supported for seven years.
Red Hat may want to spend this time convincing its customers that KVM is a better virtualization engine: Virtual Machine Manager, for example, has been already re-categorized as a desktop user interface for managing virtual machines.