Many (most?) indie mac apps use Sparkle (http://sparkle.andymatuschak.org) to autoupdate. It's generally easy to use, so most people don't need to go the microsoft/adobe route.
Edit: Very interesting! The guy behind Sparkle (Andy Matuschak) is actually an Apple employee, working on UIKit! http://andymatuschak.org/
> By day, I work on UIKit to help other people make things.