It's actually more of a hack to deal with malformed GIFs and goes directly against spec. To address GIFs where each frame has a 0 frame delay, most GIF decoders implement a minimum frame delay value.
GIF performance seems improved in safari, at least in 6.x, though this is just anecdotal evidence. The GIFs with 0.02 second frames (the actual ones, not just the "here's what it looks like under x browser" ones) seem to render with the same frame rate for me in Safari and Chrome now.
