Not so. In a Windows environment, \\ip_address\share\dir\filename is a perfectly valid argument for open. (Tested.) It isn't a Perl feature, it's an OS feature. Unix has a similar feature: NFS.
Comment on Re^2: can't open file from another machine
That's what I said: it's not open() and something else has to let you open the file like that. If the local or remote machines aren't set up for that, Perl isn't going to do it for you.