ledge guarding in brawl

[spiff-ssbb]

i havent played the game so this is a thread to help me i hope. i've seen a bunch of the pro videos and in the instances where they would normally ledge hog in melee they simply concede the ledge to the recovering character. i am wondering why they do this. i am aware that one can attack after a recovery move now but as far as i know you still cant grab the ledge mid air attack. so even if the hogging character were to be knocked off the ledge would the recovering character not fall to his death because of the fact that he must pass the edge before attacking the character on it? i just dont understand why its not possible to sacrifice a little damage for a ko like you could do in melee
for ex:
a marth is recovering and a sheik is hogging. marth is below sheik and up b's. sheik drops off ledge into a n air. marth dies and sheik gets hit but recovers. thats how it happened in melee. why does the same principle not apply to the ledge hog in brawl? someone inform me please