How many people (in your own opinion) do you think sign up to HoL and then not post. Not that it matters, but what a waste of time, just randomly view the last few pages in the 'Members' section if you want to get an idea.
The 1970 thing is a known phpBB (or database system?) bug and in case you were wondering, it is not the policy of management to delete "unposted" users. A name and info takes up dick-all space in the database and creating and regularly running a script to delete them all is just a waste of time. It also disadvantages those who create an account, just so they can use cookies and lurk.
Not that you need an account to lurk of course, but if you want to post a witty rejoinder, then it's nice if you're already logged in. The majority of people come here to ask a question in the hints'n'tips section and then leave after making maybe a dozen posts.