Why is this necessary at all? Why does every program have its own updater, some of which are even resident? Why can't the OS just do all of this for us? Linux and the BSDs have package managers, but there's a solution just as easy for the rest/majority:
Both Microsoft Update and Apple Software Update could be modified, very simply, to read updates for additional software from signed RSS feeds, and queue them into a background downloading service (on Windows it's called BITS, I'm sure OSX has an equivalent) when they see them. There would need be no central repository; each software package installed would simply install a subscription, and a public key for checking against it. The updates would all be installed in the operating system's "update mode" that starts after shutdown, negating any worry of updating a running program. It wouldn't even need to trouble the download centers themselves—the RSS subscriptions could be torrent containers, and every PC could be configured to serve as a peer.
Now, if it were me, I'd move the Mobile App Store from iTunes to Software Update on OSX and make it into a Multi-platform App Store, and create a similar store for Windows in their own update service... but that's perhaps, as they say on the Internets, "too much win."
... could be modified, very simply, to read updates for additional software ...
It's only so simple when you have a single binary file with no dependencies running only on the developer's machine.
Beyond that, it's quite a complex problem. I could give you a list of about a thousand major problems that need to be solved to make a "one size fits all" updater. Plus, it's not in the self interest of either Microsoft or Apple to allow update installation from unverified sources.
... similar store for Windows in their own update service ...
The store has been tried before (once by MS, many many times by 3rd parties). Each time it was a failure. Largely due to the uncoupled nature of the "Windows ecosystem".
Sparkle (http://sparkle.andymatuschak.org/ ) seems to be becoming a de-facto standard on OSX, and I'd say it does a pretty good job when judged against the points in the article.
I think the update-at-shutdown isn't such a great idea, most programs don't need the computer to be restarted after they update.
Sparkle is just awesome - and I really wish Apple had the guts to roll this sort of thing (if not simply roll Sparkle in) as a standard recommendation for all apps.
The problem isn't so much that apps are rolling their own updaters, it's the fact that these updaters are often extremely heavy-weight but aren't justifiably so.
I actually agree with you, completely. Many times I've wondered why we need this complex, inefficient mess of individual programs doing what a central system could do better.
But nonetheless, for now that's the way things are. Might as well do a good job in the meantime.
Both Microsoft Update and Apple Software Update could be modified, very simply, to read updates for additional software from signed RSS feeds, and queue them into a background downloading service (on Windows it's called BITS, I'm sure OSX has an equivalent) when they see them. There would need be no central repository; each software package installed would simply install a subscription, and a public key for checking against it. The updates would all be installed in the operating system's "update mode" that starts after shutdown, negating any worry of updating a running program. It wouldn't even need to trouble the download centers themselves—the RSS subscriptions could be torrent containers, and every PC could be configured to serve as a peer.
Now, if it were me, I'd move the Mobile App Store from iTunes to Software Update on OSX and make it into a Multi-platform App Store, and create a similar store for Windows in their own update service... but that's perhaps, as they say on the Internets, "too much win."