Well...it seems that many Windows versions/functions...don't need more than 8MB of RAM.
The additional amounts of video RAM have been added to accommodate visual effects/functions which have been included to deal with 3D, games, and other functions which stress motion and the depiction of such. IMO, the vast amounts of RAM which video cards have today (I remember having 4MB video cards with Win 98) are probably due to the increase influence of gaming and the eye candy which MS seems to love so much now (IMO).
You can see a more detailed view at Video memory mysteries - http://www.dansdata.com/gz014.htm
For the things that a casual user does on a PC...8MB still would work fine, IMO. I believe that gamers are the major group who actually experience the real values of the video graphics we have today, the rest of us are just unknowing beneficiaries of capabilities we will never exploit.
You may find this interesting, http://www.directron.com/howtochoosvi.html