Annoyingly, I've seen some networks that try to "fix" problems by letting that go through even when not logged in. I'm pretty sure it had been fixed last time I flew, but Qantas in-flight WiFi used to be one example I'd seen. You'd connect, and then nothing would happen and no SSL connections would work. You'd either need a non-HTTPs site to get the redirect, or go to 'wifi.qantas.com' to accept the terms and conditions before you could browse. I was trying to work out why my iPhone and Mac weren't popping up that page as soon as I connected, and bizarrely captive.apple.com came up with 'Success' instead of redirecting, which means they must have misguidedly put in an explicit rule to let that through, completely breaking the feature!