The idea is the above, to keep spammers out, and in theory, they're supposed to be easy questions anyone who's read the blog and wants to participate in the community should be able to answer.
This was the case when they were set up (forum launched in Feb 2012, blog was less than a year old, itself launching in April 2011), as anyone who had read to that point would know them.
Now the facts asked are mentioned less often, and there's way more articles, so they've become a bit tougher for someone just stumbling on the site and having read just a few articles.