Apple wouldn't give access for some hardware apis to Adobeso stuff that was being done on the graphics hardware in windows had to be done 100% software on Mac. Then Jobs complained that Flash was slow.
Try WebGL on any Mac (Safari is the worst performer of them all btw). You will see a bit of lag, frame drops, CPUs at 100%, a lot heat and your battery will die in two hours max.
Open the same site on a Chrome/Windows machine (with comparable specs of course) and you don't see any of that trouble.