They're not needed anyway when registrations are moderated and guest posting is nowhere allowed.
Already commented on area51 that should be part of the installation of an efficient CAPTCHA. It does not take 2 minutes to get a reCAPTCHA key.
And what would you use as a question/answer? If it was hard coded then every boy would know the answer in no time at all
You never used the Q&A option before? If you had, you would know that there is no hard coded questions or answers. You have to create them! So if it works or not is based on how clever someone can create their own questions and answers. Then the rules to follow, to make sure spam bots can't get past them, are very simple.
Been using it for years - but how do you propose setting it as a "default". Many/most new users would not have the first idea as to what to use as a Q&A when installing a board and would therefore add a silly questio such as "What is 2+2?" which would be as useless as having no CAPTCHA at all.