My macbook uses 2GB RAM with nothing on

So I just upgraded my MacBook Unibody late 2009 from 2GB ram > 4GB ram. I did this to improve some game performance (Sims 3) because I can't even play it with everything on low settings.

Now I start up Sims 3 with my 4GB ram but its still crappy! So I checked out my Activity Monitor and i saw that it uses almost 3GB memory with only safari on.

I attached a screenshot (its dutch).

I dont know alot about these kind of stuff so I hope that someone can tell me if this is normal.