I don't understand how the anonymous blog author identified that this is feature new in "Mountain Lion" specifically, as this is a window.webkitNotifications is

I don't understand how the anonymous blog author identified that this is feature new in "Mountain Lion" specifically, as this is a window.webkitNotifications is a javascript API introduced and adopted only by WebKit. In other words, my copy of Chrome 20 running in Snow Leopard runs this site example fine. I think he/she meant it's new in Mountain Lion's Safari.