In modern software design, the assumption that users are morons and shouldn't be allowed to do anything with their system tends to get more and more popular. This policy is certainly well-founded and complemented by plenty of experience, but in some cases, the results are at best humorous or just plain bizzare. The best-known example is the warning of firefox upon an about:config request:
I guess that's intended to be funny. Geek humour or something like that. Seen better, though. And most people find it simply annoying.
This example, however, is nothing compared to what Mandriva does to its users. Undoubtedly, the heart of any Linux distribution is its package management, and the sources (or repositories in Ubuntish) are its veins. In Mandriva, the GUI for configuring the software sources is drakrpm-edit-media:
See what I mean? The essential possibility to mark certain sources as "update" is greyed out. Even drakrpm-edit-media --help doesn't provide any helpful hints as to how to change this ... limitation *g*. That's because it's not a bug but a feature.
Now you are an expert.