just remember that the single most impactful, game-changing, and profitable revolution in web uis in the last ten years was the dramatic simplicity of the google homepage...DESIGNED BY TWO UNIX SYSTEMS HACKERS!
The legend of the Simple Google Interface.
Not saying it's not true. But are we sure we have a cause-effect here? Sure it worked, it was liked. Bu if they had a different UI, would they be nowhere now?
Perhaps there are UIs that would have resulted in faster growth or more total marketshare, but there are definitely UIs that would have made things far worse. I think the "headroom" for growth is pretty low, there were so many competing services then, if you can remember, that I find it hard to believe that there was only Google with a different looking interface.