If you're bouncing a plug on or close to the bottom, wouldn't the belly treble have more of a chance to snag than the tail siwash?
I always have them pointing down, but I guess its really just personal preference. I would assume always having it down would generally have a better chance of hooking the fish through the bottom lip instead of through the top.
my .02, with all the current, bouncin', banging and the like, i think you'll get'em if you are meant to either way your hook is, up or down. (BTW mine go either way, some up, some down)