Arcansi, here are a few examples of matches we can do for me to prove that a ledge grab limit is required (assume no ledge grab limit in these examples):
I'll go Marth, you go Falcon. I will spend the entire match on the ledge, repeating the exact same thing over and over again all match long (no difference at all, no matter where you are). I claim that you will not take a single stock off of me (we can do the match if you wish).
If you want even more pain, you go Falcon once again, I'll go GaW. From the start of the match, I will grab the ledge. From then on, I can no longer land on the stage, and my only contact with the stage must be on the ledge. I claim that I will win this, and once again, you will not take a stock (and I think you won't even damage me).
The ledge grab limit is in place because in some match-ups, it can make the matchup completely unplayable for one character. If you disagree with my examples, lets play them out next time we face each other.
And Arcansi... something I find very ironic. Melee and 64 players all make fun of brawl for two main reasons: No combos, and no advanced techniques. I find it very ironic that you are trying to remove what little combos brawl has (melee has chainthrows perfectly legal, 64 has chainthrows perfectly legal). Why is it so bad that brawl be forced to remove all their chaingrabs?
Oh, and my source for my claims:
Marth can ledge drop forward air (invincibility throughout the time he is vulnerable, while attacking anyone close to the ledge) into immediate up-B back onto the ledge.
GaW ledge-drop double-jump nair/uair, up-B back onto the ledge (sometimes up-B isn't even required).
My source for my claims that melee and 64 players make fun of brawl for lack of combos and lack of techskill: the entire melee and 64 community. Ask them yourself.
My source for melee and 64 having chainthrows completely legal: check the ruleset. Both have all chainthrows legal, including melee wobbling last I checked.
For any response you do to this post, include sources. If you are forcing us to source our statements, you should therefore be forced to source your statements.
Edit: Big D, that was actually already fairly well-known (or at the very least, assumed or almost confirmed). Not everyone has the frame data, but we know that some characters are virtually invincible on the ledge.