I'm guessing that you also think web apps are also not ready for the average user? After all, there you don't even get to have a say when the upgrade happens. And you have no way of delaying, cancelling, or undoing it.
As far as users are concerned, random stuff changing for reasons unrelated to their actions are all the same.
Does that matter? In both cases, stuff still gets changed under you at more or less random times. With web apps, you don't even have control over when random stuff could possibly change.
In Linux terms, that would be like your package manager constantly and silently updating everything in the background all the time. How dependent or independent packages are doesn't matter in this sort of scenario.
I'm not entirely sure that it makes much of a difference. Chrome shows that gradual silent updating works for local apps. Linux needs to handle that better, sure, but I think that's the way to go.
Gradual silent upgrading is poised to be a huge problem for users and yet another reason I stay away from Chrome. You should never impose an upgrade on a user, at most just strongly suggest they install and make it easy if they choose to do so.
Upgrades have the potential to break things users may find critical. Say for example in a browser, User A uses a plug-in that they find essential to their daily work and it hasn't been updated to the latest release (developer is on a sabbatical roaming the world for 2 months). Now you force an upgrade to their machine and you break their plug-in leaving them with no recourse. This is only one slim example but it's potentially a huge issue. A couple years back a Windows auto-update once killed a client's server for 2 days until I could identify the culprit. There at least I had recourse to uninstall and reject the update, with something like Chrome I don't.
In a web app things don't inter-relate the same as they do on a local OS so it's mostly a non-issue outside of user experience. Forcing upgrades to locally installed software is just asking for trouble all around.
Chrome's updates have been nothing like KDE4 or Unity or Gnome3.
Also, people have also revolted against and deserted versions of Web Apps like Digg v4, so it's the experience that matters, not just change in general. There should be no need to foist updated versions of other apps just to get a version of another app.
As far as users are concerned, random stuff changing for reasons unrelated to their actions are all the same.