I hate the thought behind this. Often I don't maximize to see more content, but to hide everything else. Why does Safari decide for me that the window can't be any wider? That doesn't make any sense at all.
Note that this concept predates the concept of maximisation, and comes from an era when single apps would be implemented in multiple windows. E.g. the content area the toolbar in photoshop were separate windows. Back then it made a lot of sense. But I agree it's just annoying now.
