Lets not forget, 8 GB is not very expensive to pull off. In addition the more RAM installed the higher your bandwidth, lower your seek times, and just becuase a game can only allocate 4GB of RAM doesn't mean windows isnt using any or your browser. On top of that Windows won't use the page file as much meaning faster load times and smoother operation over all, and if you use an SSD, longer life span.
Also be sure to note your GPU can use up to the amount of RAM it has to comunicate with the CPU, a card under full load on average uses at least 1 GB of your system RAM in order to operate at full speed.
4GB is not enough anymore, and almost every one has a 64bit OS on their PC. You need to consider headroom, if you remember on your last 4GB PC you had the more you were running the less RAM you had available the slower your device got.