Why is upgrading from 11.0 to 11.1 difficult?

From what I read, you can’t upgrade from openSUSE 11.0 to 11.1 simply by switching from the 11.0 repositories to the 11.1 repositories. Why not? I don’t doubt that it’s true, but it goes against my mental model of how software management in openSUSE works.

It seems to me that any part of the system can be upgraded: everything from the kernel to gnome bundled applications to third party applications. And these upgrades come about through teh software amangement system knowing how to upgrade rpm packaged software. Every individual rpm in the 11.1 repositories knows how to upgrade itself from the version that was in the 11.0 repositories.

So if I point to the 11.1 repositories, my mental model states, it will just upgrade all my currently installed packages to the latest and greatest that are released with 11.1. And that will be the same as having installed 11.1.

What is wrong with this mental model? What is there in a distribution that is not part of the RPM package management system?

Thanks for any insight you can give me on this. Helpful comments such as “it is a good idea to wipe your hard drive and reinstall every 6 months” are not really part of the question though.

http://en.opensuse.org/Upgrade

Still it does seem to be a tad harder then it is on Ubuntu, as on Ubuntu when going to version A to version B the process is made simpler by the update manager.
No need to manually add or edit repositories, Ubuntu does it automatically.
One of the reasons why I think Ubuntu is so popular

My understanding (which may be flawed) is that it’s basically an accident of history.

Some distros were floppy / CD based for longer, while others forged an early path to downloading packages from repositories.

Correspondingly, some package management systems had more work done on ‘hot upgrades’, while others had their attention focused elsewhere.

There’s nothing intrinsic to the packages that means you can’t do it; the question is whether the package management interface has well developed scripts which will deal with configuration files, removing unneeded stuff, potentially even changing filesystems.

Debian does it better, but the others are catching up.