While modern web browsers today may support WebGL, there's far too many computers not using a GPU that supports WebGL. For example, my 5 year old business workstations that run the latest Ubuntu.
On-hover WebGL effects only work if you fallback to a static image (an image of the non-hover state) for browsers that don't support it.
"Note that, in this demo, I assume the visitor is using a WebGL-enabled browser. A better practice would have been to first implement the page with static images to ensure basic functionality for everyone, then add the 3D effects as a progressive enhancement for advanced browsers."
On-hover WebGL effects only work if you fallback to a static image (an image of the non-hover state) for browsers that don't support it.