To remove a file you need write and execute access to its directory. You do not need access to the file. The mode field in the ls listing of a file is ten characters, one for object type, and three each for owner, group, and other. The ls command with the options -Fal shows you most of the interesting information about filesystem objects. A hard link cannot span filesystems.
Directories sometimes migrate between filesystems without users being aware of the changes.
This generally would cause the linked file to actually be duplicated. A symbolic link is a special kind of file that contains as data a path to some object, which may be in another filesystem. A symbolic link can point to a directory. The path in a symbolic link may point to an object that does not exist. This is not checked when you create the link, and nothing tells you when the object is moved, renamed, or removed.