I'm willing to bet a large portion of that RAM isn't Active (so it's Inactive), meaning it's not needed by anything else now, but if that changes then OSX will gladly realign it with whatever needs it most. This is a sign that you've had Safari open for a while and that you aren't even getting close to using all 2GB of RAM at the moment. So long as you're not seeing tonnes of beachballs, I wouldn't worry too much about it. As the illustrious WildCowboy said, restarting it will bring it back to sane levels again anyway. 🙂