That's hard to believe when many companies offer a support@company.com, twitter, facebook, phone or other means of public contact.
And why would every visitor contact the owner of the website? Have you ever sent email or wanted to send email to Comcast, Microsoft or any other interesting company? I would imagine only a small number of people would ever contact or even want to contact reddit administration (simply because the subreddits are managed by other people). And I'm sure 90% of those who contact reddit could be replied with pre-typed message of "We have no control of the subreddits - please contact the subreddit moderators".
Personally I couldn't find Twitter's support email. Tried out this page, but all I'm getting is a bunch of contact forms: https://support.twitter.com/forms ; Facebook does this too and here's the thing - they've got an automated system that aggregate issues and bubble up popular ones to their support crew. The long tail of that support queue is most probably completely ignored.