Yeah well, its a much more limited set of drivers. Essentially turns it into essentially running as an appliance which increases the reliability by "accident" with limited virtual hardware to worry about. For business use where running Windows reliability is critical, that's my absolute preferred setup for the last 3 years with Ubuntu on bare metal and Win7 in a VM. Win7 rocks in a VM. On my "old" Thinkpad W510, it booted in a VM in 20 seconds, and a year later still booted in 20 seconds which matched the bare metal boot speeds. The folks booting it bare metal had boot speeds that had slowly gone up to like 40 seconds to a minute.
Currently Win8 doesn't run well in a VM due mainly to the UI, but maybe they'll get that fixed before release. Too much corporate IT using VMware View and other solutions (like VirtualBox) to not support it.
The reason I said the Win VM running well being suprising, is because NT4 through XP had issues due to a bad driver model that put too much into Ring0 (like video and printers in particular). When you have a VM running in Ring3 and the Hypervisor having to thunk the instructions back and forth, it slows things down remarkably at least until Nested Paging support, but even then Win7 is still lighter than XP. Now that MS reverted back starting with Vista to the NT3.51 driver model (more or less) with most drivers back in Ring3, the speed of it running in a VM is much improved over XP. The less Ring0 drivers the better, not to mention the "perceived" multitasking performance is improved with multicore machines. So put in that perspective, its not suprising at all that Win7 runs great in a VM. Limited hardware combined with Ring3 drivers equals good virtual performance.