Can someone explain why HTTPS is necessary for a webpage where I don't log in or submit any information?

For example, take the xkcd homepage. Not only do I not log into it, there's nowhere I _could_ log in. The only input is a search box (which seems to be disabled at the moment anyway). Is it really a security risk if my communication with xkcd's servers is unencrypted? (Yes, xkcd has a store and a forum, and I understand why you'd need HTTPS on those subdomains - but I don't see why the main domain needs it.)

I agree with the parts of their plan to disable browser features that could be a security risk to non-HTTPS pages - that makes total sense. But it seems absurd to prevent static pages from using future CSS layout features just because they're not using HTTPS.