Well, the development cycles are different, of course. GC has started out as a very simple 'Graphics Converter'. More and more features were added over time.
The many releases mean both that he includes many new features and that bugfixes *must* come out, because as a user you're basically also a beta tester.
It's a shame though that Adobe doesn't usually evolve their versions. InDesign is the big exception, which got more features with 1.5.2. Normally a 'final build' of Photoshop or Illustrator has a very, very long X.0.1 life.
But that's just the difference in marketing strategies. GC's image *lives* from being small with incremental updates. So does, for example, OmniWeb.