enigma1 - 3:46 pm on Feb 14, 2012 (gmt 0)

I was led to believe that it was 'reasonably bad database practice' to be storing the same info twice

Depends what they do. I haven't checked the code but if you wanted to search posts along with the poster name and/or the poster has closed his account, you would still want to find the relevant posts. So the post table would keep information about the poster at the time of his post. It's history recording and not always the same as what's in the current members table.