It sound nonsense, but it's the truth.
I can easily use up almost all 3G of my VRAM by just using Safari -> Facebook. And I can easily release most of the VRAM by just close Facebook.
At the same time, you can see that the system memory used by Safari didn't change that much.
You can test it by yourself. Even though iStat call it processor, it's actually the VRAM usage, they just change the name in the current version, but still monitoring the same thing.
In fact, all Chrome, Firefox, Safari, etc... use GPU acceleration long time ago. You just didn't notice it. And some browser like Chrome, you can actually turn off GPU acceleration to avoid it use up all your VRAM.
http://www.chromium.org/developers/design-documents/gpu-accelerated-compositing-in-chrome
Try it, and then you will know the truth.
Another test, but using OpenGL Driver Monitor to monitor the VRAM usage.
