(I do not have any particular problem with that, just curious)
The kernels used are not your normal kernels that are shipped with the distros. The domU kernels need patches from Xen in order to work under Xen, and the newer kernels require pvops support enabled. Latest-2.6 still points to the last domU kernel because there are still some small bugs with the pvops kernels.
so you mean there is an issue with xen/pvops and in newer kernels pvops must be enabled for xen to work correctly?