It's not a behind paywall, it's a free site.
Sites that do not require payment still need to distinguish between users that have registered and visitors that have not as well as between users, such as for comment sections (are you LordWabbit2 or someone who Firesheeped his session cookie?) or "free reg. req." policies.
What network administrator in his right mind would hand out the root certificate to the HTTPS proxy?
Anyone who wants his users to know they are connecting to the correct proxy. Remember that a root certificate contains only the public key, not the private key.