A better interface feels better. Looking better certainly doesn’t hurt but a gorgeous looks cannot make a broken interface.
I have never found a better way to create a great feeling than mere trial and error. Maybe it is that I lack that certain flair, that innate talent which prevents me from coming up with the right thing the first time. But in all of my endeavors to create a good user interface, nothing has yielded better designs that tweaking things over and over again, then a bit more.
That is why I am somewhat opposed to designing things in Photoshop. Photoshop is useful for creating a look, an identity for your project. But past that certain step, Photoshop is just what it is; it’s a graphics tool, not a development one. You cannot iterate on it, especially with live data.
At the end of the day, the person who ends up affecting a great deal of, if not most, how your users experience your site is the person, or people, who will keep iterating on that design; be it your front-end developer or UI engineer, or whatever the term du jour is.
That probably sounds self-serving. Of course it does; I wrote it. However, the point isn’t that some people are more important than others.
Developing a great interface requires a great team effort (or great people with different skillsets). The manifestation of your product to the eyes of millions is too important to be left to either just a designer who never touches the code or the developer who has no respect for what he is working on.
On a related sidenote, I really wonder what the internal culture is Apple like. How do designers work with developers to create those interfaces? Something tells me that creating those one-off things like Time Machine or the Interface Builder’s rotating iPhone window must not have been easy, requiring crazy hacks. I can imagine, in another company, developers pulling their weight and just saying those are just too hard to implement.