The difference is that those APIs are "non-cloud". The code necessary to run those APIs is spread far and wide and no one can just centrally "turn off" .NET or POSIX. Perhaps over time the programs written for unmaintained APIs will fail on newer platforms, but you will always have the means to go back to the old system and run your dependent programs there. In Google's web-based system, Google is the only one with the keys necessary to keep that engine running, and if they take their ball and go home, all of that API's users are screwed.
