don't they still end up somewhere though?
Yes. As a matter of fact I recently found my dead horse, Frost, still happily bobbing in a stream about a 5 minute swim from where I launched his corpse after he was killed by bandits at the start of my game. For refference, since this horse was killed I leveled 43 times, became head of the college, the companions, the DB and the thieves guild and it still hasn't rotted away. I'm guessing eventually my save file will become buggy or corrupt because there's a ton of dead bodies bobbing away in various streams. Why did they have to add a current to the water, I just can't help myself :/