This may seem like a stupid question, but if the rules for gallery submission state that :

"No work in progress. We're not too strict on this one... just don't throw up junk you spent a couple of minutes on or a half finished piece." 

how come people update, improve and change works that have already been approved?

basically, if you post something you half assed, and people suggest something and you just keep going along those lines, it will get revised. 

even more simply, if you are done with it, submit it.  if you are still working on it, dont.

updating every now and then is just fine, but updating every few minutes, hours, or days isnt.  and everyhing is logged, so us admins know if thats whats going on