To retrieve sections from archive, why do I need read/write access to the Arc directory but only read access to the archive files?

Earlier releases of the system would open the archive only if the system detected read/write rights. In version 10.0, this was changed. From version 10.0 onward, the system tests to see if the archive is read/write and if it is, it opens it that way. If not, the system opens the archive in read only mode. This lets you set up your rights any way you want.