(I see the author of the piece you quoted has responded also.) Really, it's not just the SOC. As described in @mikeash's piece, the 64-bit address length has

(I see the author of the piece you quoted has responded also.) Really, it's not just the SOC. As described in @mikeash's piece, the 64-bit address length has allowed Apple to inline some per-object information (like reference counts) with object pointers, which is a big win in some key operations (2x faster object creation/destruction), which could sometimes make a big difference at the application level.