@WereKitten - you obviously haven't had the privilege of being attacked by the "antivirus" virus. That comes in through normal web browsing, and I see it almost every day @ my job. It affects pc, mac, and linux so it could possibly infect ps3/wii/x360.
If the browser does not allow executing software from the web, then there's no way to be infected by a virus unless someone finds some very specific kinds of bug in the browser itself. In normal web browsing there's two kinds of software you want to run: Flash and JS. If those two engines are coded so that they have no direct access to the hardware or HDD, then the worst they can do is crashing the browser itself, but they can't cause any permanent change on the machine.
Really, it's that simple.