Take a look at Mac programs, for example. For the most part, they all have menus, windows, and title bars that look the same. But the important parts of many apps are unique. This makes things easier for both developers and users.
Imagine, as a developer, having to code the entire UI from scratch every time. That's how it used to be. It's not so nice for users when every app looks similar but it subtly different. It means every app has a steeper learning curve.
I think there is room for both uniformity and creativity to co-exist.