A snapshot of Build Windows Keynote #1 presentation
To do comparison, both plain Vanilla Windows 7 SP1 and Windows 8 Developer Preview Edition were installed on two identical computer hardware. And I have captured the Processes and Physical Memory usage for both Operating System during system idle and it is quite closed to what has been announced.
Processes & Physical Memory Usage on Windows with 7 SP1
Processes & Physical Memory Usage on Windows 8 Developer Preview