Duh!: I'd previously hypothesised that Leopard's delay meant Apple must be working on virtualization features, but I guess I was wrong. But that in its own right confirms another growing suspicion I've had, about OS integrated virtualization...
Instead of virtualization, Boot Camp, the feature that allows Windows XP and Vista to be booted on a Mac (serially - without virtualization), is now in Leopard. You still have to shut down Mac OS and boot Windows XP or Vista separately, but Apple confirmed that it is still friendly with Parallels and VMware.

Here's the lesson: Maybe there's a common theme to be observed in the struggles of the major OS Vendors to get new versions to market and the state of their current virtualization offerings. Within the last two months, we have seen the long delayed release of Red Hat's EL 5, with a "Linux only" implementation of the Xen hypervisor (and plenty of gotchas), Microsoft's recognition that combining a hypervisor with a major OS release is extremely difficult, and now Apple's struggles with Leopard and .. no virtualization.

And here's the theory: OS Vendors have so much on their plates just to get the OS to market, that their virtualization offerings will always lag behind - almost as an afterthought. Though it is technically feasible to deliver a hypervisor integrated with the OS, in the case of EL 5, Xen is only one of thousands of components in the release, and vendors have to focus their resources on the whole package. Indeed it's not reasonable to expect them to do a good job of virtualizing and supporting their competitors' products. This makes it highly improbable, for example, that Novell's SLES will do a good job virtualizing Windows or, for that matter EL 5. Novell's expertise is Linux and Netware - not optimized I/O for SQL Server on Windows Server 2003!

Nutshell: Virtualization platforms (VMware ESX, XenEnterprise) developed by vendors solely focused on virtualization as a platform feature, will lead in multi-OS performance, features and management. It's true for VMware, and certainly true for XenEnterprise and our (free) XenExpress for Windows and Linux.

Am I wrong again, or does this make sense?