You (as a developer) could scroll by 1px to remove the address bar in iOS6. It was useful to give your page it's own top navigation or just have more content visible. That was not possible in iOS7.
So you want to fill the user's limited screen real estate with your own useless crap (usually "download our app and subscribe to our emails!"), and you're worried that the actual functional bits of the browser are getting in the way of your doing that?
There are plenty of uses for fixed navigation that aren't spammy attempts to force app downloads. Users like them. Not all users, but most.