Why do amp A-B switch-boxes have a watt rating?

Okay, I know that it's not the best thing in the world to have anything besides high quality speaker cable in between my amp and speakers, but my work as an audio engineer necessitates me having multiple pairs of different speakers at the ready.

Why do the A-B boxes that I see being sold have ratings such as "can handle sources up to 100 watts"? If they are just passive switches, what is the rating all about? Isn't it just making and breaking a connection - sort of like touching speaker wire to binding posts? In that case I would think that there should be no limit to the amount of watts that can pass through. Speaker cable for instance carries no such limit. Incidentally my amp is an Odyssey Stratos at 100wpc.