The limits were probably introduced due to
feedback spamming by some trolls which I think was a good move by the administrator.
I think feedback spamming could have been fought by allowing admins to delete nasty comments that don't belong on a user's profile. The way it is now, allows anyone to write anything and it will stay there. You can open anyone's profile and write "retarded degenerate" and it will stay there. Users should have the right to report such things and ask admins to remove it, no matter what controversy it might create. I have seen comments like "su**s di**" and crap like that and there is no valid reason that should stay.
But if I traded with one person 10 times, I would like to be able to add 10 different feedback entries. My experience with the other party can be different each time and I should be able to report on that in different intervals.