> The downside of this model is that developers who want to ship their new software or feature updates without waiting for a new distribution release get stuck into dependency hell and have to operate outside the normal packaging system.

When I was writing apps for distros, I had the opposite problem. Every single release of GNOME and Ubuntu would break PyGTK in some way so that my software that used zero new features in the OS, would require at least some modifications and force me to maintain many versions. Finally, Gtk changed something that broke something in a fundamental way (something in Gtk TreeView, I forget what exactly) and I simple gave up maintaining software rather than suffer through figuring out how rewrite everything again.