All defects should be eventually fixed, but its a case of priority. I am certain that the stardock stats that they collect show the overwhelming gams played are single player. Of those limited multiplayer games, I am sure the vast majority of those are co-operative mulitplayer. Do I want competitive multiplayer to be viable eventually, yes I do, but I still see myself playing more single player and co-operative muliplayer (with large numbers of AI) compared to competitive multiplayer (with few or no AI).
Therefore I feel that defects which give the AI (or certain AI races) a serious advantage or disadvantage to be stardock's highest priority. Defects which give all parties a small disadvantage can be relatively worked around by a human player, if they know about it and understand the defect. Defects which give a human player an advantage can simply not be exploited using the honor system, if playing multiplayer, in nearly most cases.
As Willy stated above, the AI doesnt know how to exploit or cheat. Humans do.