Why would connecting to WiFi even attempt to open a web page? Something is really messed up.
It's checking to see if the wifi has an internet connection or if it is a captive portal you need to log in to. If the wifi requires a log in, it shows the page it redirects you to even if you aren't in a web browser. Before they added this, you'd be trying to figure out why your app isn't working until you tried safari and got the login page there.
Looks like the server it connects to to test the connection is broken.
I have an AT&T 4s with the same problem, After upgrading, whenever I attempt to connect to a wifi network I am prompted to "Login" to page that does not exist on apple's website. I've done the network settings reset and airplane mode and still am having the same problem.