The S simply stands for speed
Jason Snell on the lack of public iPhone specs:
The more complicated a product gets, the more technical acumen is required to put it together. Bad Web sites are built by people who know how to code HTML and JavaScript but don’t understand how people use the Web. Bad software is written by people who are experts at knowing how a computer works and how to write code to make it do what they want, but no idea about how regular people behave and how those people expect to interact with that software. Bad hardware is designed by people who choose the shape of devices and the placement of buttons based on the best way to lay out the internal circuit board, not by people who think about the most convenient ways for the human body to grab hold of that hardware and press its buttons.