The internet is international: its physical presence--while necessary--is often meaningless to its cyberspace equivalent. For example, it doesn't matter where Google locates the servers and data centers for its search service; the service is used independently of its physical location.
Jurisdiction should apply to those responsible for the content on the web (e.g. the individual or company who owns the site), not to the physical location of the host that content resides on. This is especially true for 3rd party hosting, where a single host may contain many unrelated sites.
Enforcing local US laws on foreign entities promotes bad foreign relations and encourages moving the physical presence of the internet to less restrictive areas, taking their high-paying jobs and taxes with them.