There should really be a standard for dealing with this, like a flag on DHCP saying "O HAI you need to login here", and providing a REST endpoint that will tell the OS the status of the connection at any given time.
Since an auto-upgrade to https would break a considerable number of examples, and there's no compelling business need on their part to promote https-only, it's much more likely to stay available through http than just about any other website run by commercial interests.
Host example.com not found: 5(REFUSED)
Google uses http://connectivitycheck.gstatic.com/generate_204.
Apple uses http://captive.apple.com/hotspot-detect.html and http://www.apple.com/library/test/success.html.
Both happens in chrome hence the same browser context.