The above info isn't quite correct.
The SYSTEM RAM (i.e. the DDR3 plugged into the motherboard) has absolutely nothing to do with the video cards. The TOTAL that you have is simply the total amount of all sticks. You want IDENTICAL sticks preferably (or same frequency/CAS for all of the at a minimum) and installed in PAIRS (2x2GB + 2x4GB) but the total is again just the total amount.
The VIDEO RAM is a completely separate issue. In SLI/Crossfire both GPU's have their own set of VRAM but the data is IDENTICAL because each GPU alternates which frame is sent to the screen (Frame#1 from GPU#1, then Frame #2, from GPU#2 etc.)
So yes, the VRAM amount that compares to a single card is still 4GB if both GPU's have 4GB each.
Summary:
So again, he's correct on the SLI portion and TOTAL system memory separately, however I don't know why he says "That case is with gpu vram in sli or crossfire configuration" because they don't have any relation to each other.
Basically the CPU works with the System RAM data, and the GPU's work with the Video RAM data.