While you may think so, GPL is based on copyright, and it's what the copyright law and courts say which count. Linked modules contain code covered under copyright and hence is regulated by the GPL. A connection via TCP/IP does not.
It would be odd indeed to connect to Facebook's web site via TCP/IP, and claim that the Facebook system and my TCP client code are all part of one system, so Facebook has violated my copyright.
If you're curious about the legal side of linking in non-C languages,
the following legal analysis of the LLGPL (Lisp Lesser GNU Public License)
is an interesting read:
It would be odd indeed to connect to Facebook's web site via TCP/IP, and claim that the Facebook system and my TCP client code are all part of one system, so Facebook has violated my copyright.