This made me curious about S & B on JLA covers. I looked at the Grand Database, and it looks like they don't appear on a cover at all until #19! One can also tell when Batmania struck, because he was featured on every cover for a couple of years.

I seem to recall reading why they did that - promoting the less popular characters? not overexposing S & B? - but I might be conflating that with the JSA in All-Star.