[kelnos]

I think for the case of the home router admin page (or really any admin page on your local network), the browser can easily detect that it's being served a page on the local net, and could provide a less scary warning that has some text that acknowledges that you're on your local net and that either ignoring the password form security warning (for http) or accepting the self-signed cert (for https) is probably ok. Whether they'll do this is another question...

[Whitestrake]

It absolutely makes sense not to display warnings that HTTPS isn't in use in circumstances where HTTPS is not feasible - i.e. local addresses. It's simple enough for a browser to determine. I don't think conditionally accepting a self-signed cert is necessary.