Take a look at WebKit.org for a second. They're moving fast, they're changing things up at an insane speed at times. On a Mac, just throw Nightly on there and see just how much better it is to be able to run the latest build. Weeks and weeks pass by with no update to be seen on iOS, unlike OS X where you can just run the Nighly like I said. I'd like it Safari was updated on a monthly basis, and likely not tied to a version update, but that's not likely to happen.