Ive's team used Helvetia 45 Light but not to be found anymore. Wht happened?
They dropped the Light font replacing it with Regular in July 2013 - following lots of criticism from the design community that they were putting style before substance and sacrificing usability for fashion.
Here's a writeup of the change.
It's impossible to know for sure if the criticism was the reason they dropped it, but it was one of the biggest serious criticisms of the early preview (alongside taste-based criticisms of the rainbow gradients, and general surprise at Apple making an about-turn to follow a trend led by their competitors).