Earlier quoted context omitted.
Apple will never implement anything in a browser that could make a web app as capable as a native mobile app, they are simply too greedy. Firefox typically doesn't implement these things unless they have to because they don't have the resources that Google and Apple do.
I hadn't thought about this angle as to why WebKit hasn't implemented this, but yeah 100%.
Apple is also on the W3C committee that approves new specs, where they abuse that power to prevent any spec that might cut into their app business from moving forward.