From Chris McCosky's blog:
Joanne Gerstner was at Bulls practice today and she reports that Ben Wallace sat out with back spasms. She said he was walking real slowly, clearly uncomfortable. They will determine his status at game time, but Ben not being able to play might not be great news for the Pistons. They have been able to put heavy pressure on the Bulls' perimeter players, largely because they don't feel they have to worry much about Ben or PJ Brown down low. If Ben doesn't play, Scott Skiles would deploy a small lineup, with five scorers -- the kind of lineup that has given the Pistons problems at times this season.
I have a hard time believing that Ben Wallace sitting out would be somehow beneficial for the Bulls. I see where McCosky is coming from, but without Ben Chicago's lack of size would be exploited by the Pistons' big men all night long.
In any event, it's probably a waste of time even thinking about such scenarios -- apparently Ben is expected to play. Especially considering the amount of abuse he's taken for apparently going soft against his teammates, can you imagine him actually sitting out a playoff game? Neither can I.