This is my everyday computer, no special prerelease software installed. I run Safari 7.1.7
Just uninstalled Flash to test it. No change at all. Turned off extensions completely. No change at all. Even editing in this textbox jumps to 30% CPU usage. I do only observe this behaviour on macrumors.com. The vent constantly blowing gave me the hint that something is wrong.
But I really don't think, this is a Safari only issue. I really believe, the JavaScripts here are a little too jumpy, immediately firing events every 60th of a second even with the slightest change.
Firefox tops at 40%
Chrome easily jumps to 60%
Opera about the same as Safari
Tested it on Snow Leopard as well. Same thing but even higher when scrolling as there is no GPU scrolling.
Testing on El Capitan is slightly better when scrolling. Perhaps due to Metal.