But VRAM is included in the memory addressing for Windows. It's why on 32 bit that having a graphics card with more VRAM will limit your system RAM since the memory address is limited. The same applies to Windows 7 Home Premium 64 bit. Even though it's 64 bit, the memory address capability is reduced which would mean that it is effected by the graphics cards.
Nice read on memory addressing:
http://www.tomshardware.com/forum/258528-30-explained
The same concept of a reduced memory address on x86 applies to Home Premium 64 bit.