I have my adjusting housing on the opposite side to the chain Craig, as this is same side as it was when I pulled mine apart. I, like you, have wondered why there is adjustment on one side only. I'm sure the other guys will be able to enlighten us in due course. Maybe on older models there was adjustment on the chain side also & they just continue to use the slotted same housings?? One even has a coil spring inside on my set up & I have no idea why either.

Ross