[morsch]

Because currently 'apt-get update' fails hard as soon as a PPA repo disappears.

No, it doesn't:

  W: Failed to fetch http://repository.spotify.com/fake-
  url-to-fool-apt/dists/stable/non-free/binary
  i386/Packages  404  Not Found

  E: Some index files failed to download. They have been
  ignored, or old ones used instead.

All the other repositories are refreshed as usual. Again, apt-get and the rest of the underlying infrastructure is not the problem. I agree that users should not have to find a script, I'm just saying that's a reasonable way to solve the problem. The script should be part of the distribution, just like add-apt-repository, another script, already is.

(That said, I can agree that integrating this functionality into apt offers a chance of deeper integration in the future. And while it's not the Unix way, it may be that the Unix way has stood in the way of an ideal Unix desktop experience for some time now.)