I've no access to rhn.redhat.com and fedora virtio packages should belong to the same codebase, just the former should be always from "stable" branch, signed and certified. I think XP does not need "signed" drivers, since this concept was "invented" later.
If you are suggesting that Fedora virtio drivers are broken "by design" to force people use RH virtualization, or at least subscribe their RH server solution, that means that KVM outside RH is doomed.
I use GNU/Linux everywhere possible but all business needs some M$ Windows VM running for legacy apps, so not being able to provide a reliable and good performing solution is a big problem.
I.e. I've been told that vmwhere "guest drivers" are stable, work with almost all M$ OS range, and let you do more things like clean shutdown of M$ server VM even if users are logged.
In comparison for Fedora is all a guestwork, with some really bad experience (i.e. something like "test the latest and the VM will never boot again, you have to restore the former backup", or "connectivity is lost sometime" etc.).
I really hope RH is doing his best for the community as usual, and that Proxmox can make enough money to have a look at virtion code and send some patches / provide signed drivers / whatever.