The illegality (or quazi-illegality in the case of the links from the edu sites) of the mirrors is what's keeping them from being hosted permanently on a free site.
If the copyrights were clear, there would be repositories like arxiv.org that would ensure high-availability free access. The paper isn't on arxiv.org currently because Nature uses its copyright to ensure that it's not.
If the copyrights were clear, there would be repositories like arxiv.org that would ensure high-availability free access. The paper isn't on arxiv.org currently because Nature uses its copyright to ensure that it's not.