FWIW: I do video editing on this system...using both XP and Win 7. I have a total of 8GB RAM installed, with only 4GB used by XP.
When I render changes/edits...that is when the system resources are most used. Using Task Manager...I have never seen a strain on either the RAM or the CPU when doing my tasks. 4GB or so of RAM seems to be more than enough for my video-rendering efforts. I can tell that the CPU is working harder...because the noise from the CPU fan becomes more noticeable...but I've not seen any indication that I might successfully employ more RAM to render using programs that have stated specs saying that 1-2 GB of RAM will do the job.
It's the program employed that uses the RAM...I've not seen a program which demands more than 8GB of RAM for optimal performance...but I just do routine things (I consider video-editng a routine task) on my systems.
Google Results, How Much RAM
One thing to always remember about anything posted or stated on the Web...some are educated opinions, some are just BS passed on by those who don't know better. I trust my personal experiences with different systems having different CPUs, motherboards, and RAM installed...than I would trust an opinion that overstates an opinion that just cannot be borne out by documented or personal experience.