Mus, in-game a hit sprite represents multiple rounds hitting. It's a balancing act, as far as I figure. They stay there longer because when you land 10 hits you're only seeing the 1 sprite, instead of 1 micro-second sprites. Reduces work on the front end of the guy seeing the sprites.
P.S. That's not a guess, they've said before that any hit sprite can represent multiple hits, so it's not a 1-for-1 when you review films in slow motion.