Lets face it. Raiden's down throw animation to the bounce is absolutely hysterical and horrible. We all know that his forward throw was an easy break, so really; how do we fix this?
I say, do the forward throw again, but instead of crumple, put it to bounce. Having a character bounce randomly is just...kind of sad looking, and reflects on some of the lazier design of the game.
It's almost like the crushing of their spine or whatever he pulls out causes them to spasm suddenly. How, you ask? Well that's very simple.
But really, when taking into account Big Daddy's level 3, this really shouldn't matter all that much.
They did it for follow-up hits though, if you had it to where they bounced WHEN he pulled out the spine, it would completely defeat the purpose of having them bounce in the first place, since they would've landed by the time the throw ends. Of course it looks silly, but it's really the only way it could work. Plus having them bounce on the forward throw wouldn't make any more sense.