I tested this just now, I deleted one worker and my income didn't change at all. I deleted a second one, and my income shot up by 5 gold. This seems to happen with any type of unit. Unit maintenance is presented poorly, and not explained at all. We should be able to see exactly how much gold each unit is costing us a turn, and I'm hoping that it being calculated in pairs is a bug. I don't mean to heap on more negativity onto the game, I'm having fun overall, but this really needs to be addressed, considering that unit maintenance takes up so much of your income.