Safari is holding back the web with their old, quirky, outdated engine. However, as Safari's engine is the only option for iOS, most web developers can't afford to ignore Safari because they can't ignore the iPhone. So it's IE all over again - an old, outdated browser that everyone nevertheless has to support as a significant portion of the users are using it. In some ways it's even worse, as iPhone users don't have any choice due to Apple's restrictions, but even in the darkest days of IE's stranglehold on the web Microsoft never restricted what browsers you could install on Windows.

Apple is pretty notorious for holding the web back post Steve Jobs. As an example, it took them forever for push notifications for web apps on mobile (like literally years behind their competition)