Free RAM is wasted RAM. RAM is there to be used. OS X will use as much RAM as possible. That's a Good Thing.
You don't need to worry about freeing up precious RAM in order to anticipate launching more apps in the future. OS X is well aware that you might do this, and is prepared for it.
If you're running "SafariForWebkitDevelopment" in 10.8.4, then you're a developer running a test environment, so that software is probably not optimized for efficient use of resources.