The overzealous HN title will no doubt be updated shortly (currently says "NSA-proof iPhone calls to dead anarchists", should say "Free, Worldwide, Encrypted Phone Calls for iPhone".
I highly doubt Moxie / WhisperSystems thinks this "solves" the problem, as opposed to reducing attack surface in important ways. RedPhone and Signal address an important part of the convenience-vs-security pareto curve. Tapping communication lines is a whole lot easier, and harder to detect, than exploiting hardware.