Just to add to this discussion... For various reasons I can't make every game but I have been to 10 home games this season, and 2 away. So I guess I might class as a more casual supporter?
For me it makes no difference who we are playing, whether we are top of the league or bottom I will just come to whatever game I can make it too. I came to Charlton, but couldn't make Palace due to being away over easter, and I will be at the Burnley game.
I suppose my point is that sometimes there is no particular reason for people coming/not coming, so higher or lower attendances on a game by game basis could just be down to circumstance.
I also don't particularly buy into the theory that there are 5-10 thousand 'stay-aways' who used to come every game but now don't come at all. I think we just have a lot of 'casual' fans who are still coming just maybe not so often.