> A. Commenting at scale is hard. Believe me, I know.
Other than just believing you, what makes it hard? I've had to scale comments on some very high traffic websites and it was pretty straight forward. Unless it's a complex comment system, but then you wouldn't use Disqus anyway.
Building an auth system, user accounts, comment submission, moderation, and threading, then rendering all of that out is more work than it seems. All of the dynamic-ish stuff (seeing your comment immediately, noting your comments) has to be carefully thought out. Right now commenting takes half our app load, and it's pretty tightly written.
