In my mind it makes perfect sense if you just think about it a second. If you blow something up with a bomber's bombs, it increases your bomber "vs objects" hit %. If you strafe a ground target with your bomber's guns, it does not. Likewise, if you strafe a ground target with your GV guns it does nothing for your "vs objects" hit %. You need to hit it with your GV equivalent of bombs (ordinance), which in this case are rockets or torpedoes.
I think of it as "vs objects" meaning "with ordinance", while "hit %" means "with guns". More to do with the type of weapon you're using than with the type of target you're hitting.