The "occupied base" is in regards to the runner. The pitcher has to throw "to the base." Therefore, a fielder has to be at the base if he doesn't step off. In other words, the pitcher can't be in contact with the plate and turn around and throw it to the second baseman who is halfway between first and second. He has to step off first to do that. It's ridiculous to be used in this case. It also brings up the classic argument of why can't a pitcher with a runner on first, 2 outs, 3-2 do an inside move to second base? The rules state that second is an unoccupied base, BUT that you can throw to an unoccupied base (second) to make a play - runner is stealing second.