freitasm: So if your router doesn't see the Internet but you still want to connect to access an internal server... You can't?
What it actually does is load http://www.apple.com/library/test/success.html and verify that it returns "Success". The idea is that if any other HTML is returned then you're running on a public network and need to buy credit, agree to TOS, etc. It then automatically opens Safari so that you can do this.
The problem is that Safari gets "locked down" when you do this; you can't go to a site of your choosing until it gets that "Success" response. Today that address was returning 404 so it was going into "public network mode".
If you're on a closed network with no Internet access then the connection to www.apple.com will fail in the first place without returning any HTML, and it won't go into "public mode".