I wonder if the author has had anyone extol the virtues of Ubuntu at him yet... Not to sound fanboyish, but Ubuntu's package manager (Synaptic) more or less meets a lot of hit requirements. The best part is that all of the updates are coming through the same source, so you don't have to hunt down the updater in every single piece of software you install.

Of course, I say Ubuntu because that's what I know. I would not be the least bit surprised if other linux distros/mac os had similar package managers.

It seems like even windows could form some kind of agreement with various software vendors allowing them to push updates through the windows updater. Opt-in of course.