If they want to make sure their answers stick around, the authors may indeed want to store them somewhere safe, away from Stack Overflow. Many of those questions are so broad they might well get closed and deleted one day. Unless somebody is there to notice, to understand what happened, and to raise a mod flag for undeletion and preservation, the answers will simply be gone. (Needless to say I think that's a pretty sad state of affairs.)
In case it is unclear to anyone - it is perfectly fine to re-post content you write on Stack Overflow on your own blog or whatever! You keep the full copyright for your contributions and can do whatever you want with them; the CC license merely gives the community the right to use them under certain conditions.
Here's a scientific infographic explaining how it works.