Unless I am confused, "Zones" are virtual machines. If you think there is no equivalent, I guess you are not familiar with Xen or KVM, or the dozens of other VMs out there.
Yes, you are confused, which probably indicates your lack of familiarity with Solaris Zones.
Xen, KVM, VMware, Sun Logical Domains, and Sun Virtualbox, are all examples of hardware virtualisation. They simulate a hardware platform; a virtual machine. Each VM has its own kernel and scheduler and memory space and device drivers and virtualised storage.
Solaris Zones is an example of operating system virtualisation. There is no direct equivalent on Linux. There is a single kernel for all the zones. A single set of device drivers. A single process tree. Potentially a single storage system. It's extremely lightweight compared to virtual machines.
Thinking of Zones as "virtual machines" is simply wrong. They are more like process groups, or process sets, and in fact on Solaris they are implemented in part by using resource groups. There is virtualisation but it's not at the machine layer; that's why they're not virtual machines.
To illustrate the significant differences, on the same hardware that Xen can run 10 VMs, Solaris can run 100s of zones. Xen can lose 10% or more CPU to overheads, Solaris Zones loses less than 1%. Xen can lose as much as 90% of I/O performance, Solaris Zones loses less than 1%. Xen places restrictions on the resources available to each VM, Solaris Zones can gain access to the full resources of the hardware. Xen requires each VM to be patched and maintained separately, Solaris Zones are patched and maintained through the "host" OS.
These benefits are only possible because Solaris Zones are not VMs.