Hollow icons = cognitive load
Nice article by Aubrey Johnson: Hollow Icons on why hollow icons are just more work for people. This is yet another reason why the iOS7/flat design style just isn’t fully baked; removing too much affordance requires more cognitive load on the user.
His thesis: “Don’t follow bad design decisions to appease a platform.” Obviously nobody is going to consciously follow bad design decisions…but they end up doing so because they don’t re-evaluate what’s working best. When you blindly copy a style for the sake of it you skip over important questions like “Is this icon the best way to communicate this function?”.
The icons in iOS7 Safari are especially egregious, a real step backward from iOS6. But, and this is a big but, I’ve been around long enough to know how hard it is getting anything built, and so I’m joining those optimistic folks who regard iOS7 as a start, not a finish.