According to http://github.com/blog/621-bye-bye-flash-network-graph-is-now-canvas#comment_6954 http://github.com/blog/621-bye-bye-flash-network-graph-is-no...,

According to http://github.com/blog/621-bye-bye-flash-network-graph-is-now-canvas#comment_6954 http://github.com/blog/621-bye-bye-flash-network-graph-is-no..., there are too many DOM objects involved in the graph for SVG to be performant.