Well, there is another angle here from the Defense sector. Lotus Notes had a big ole backdoor in it: http://www.cypherspace.org/adam/hacks/lotus-nsa-key.html

The same problems keep being solved, and then nation-states get involved, and eventually the technology shifts to something else because the game has played out as far as it can in terms of those nation-states. It is not really so much as a steady march of technology, as much as it is a quiet kind of informational arms race.