When you expect to get most of your revenue from selling apps in the iStore - it's essential that people are unable to get apps for free via fancy web pages.
Is this because Apple can't support WebGL? Hell no! The browser actually DOES contain code for WebGL, but it's disabled...UNLESS your web site signs up to display Apple-provided advertising banners...in which case, WebGL works great!
Safari uses the exact same core rending software ("WebKit") as Chrome - so it can trivially support everything that Chrome supports - it's really just a matter of Apple deciding to deliberately cripple the browser to prevent people from providing apps for free.