BTW, Before you make any "claim" that "it doesn't make sense", allow my to ask you this:
A man is 10,000 feet in the air. He falls. 10' away from where he is going to impact is a 10' tall step ladder in the middle of a flat, featureless plane. He touches it with his PINKY and lands on his feet, casually strolling away.
That doesn't make ANY sense until you state, "It's a class ability, deal with it."
Well, you might think that because it "slows" the fall that it negates damage against what you hit. "slow" is a term that refers to how many actions you can take. It doesn't apply to falling in anyway. They did not define the class feature well. They didn't define falling well. So this is the logical conclusion of how the rules read as written. In the RAW reading of the rules, the monk not only lands unharmed, but the ground takes 20d6 points of damage at the point of impact, leaving a crater and a cloud of dust that the monk walks out of.
Now, if there is anyone here who cares to take the position that monks are overpowered, please, by all means, lets argue if this obscure method of attacking that usually takes two rounds to set up is really all that game breaking. (And yes, I've been playing with it for months. My players come up with half of the crazy crap that's in the EVD. They use it when I give them something that is utterly invulnerable to normal attacks, because falling damage gets through just about everything.)
And remember, if the target sees it coming, it's a DC 15 reflex save to step out of the way. That's why the party monk is the only one able to pull it off. Without a successful maxed out stealth roll (see the EVD Skill Handbook for combining Hide and Move Silently) Just about every target will avoid damage unless they roll a 1. (at least in my high level campaign)
Oh side note, you can only use the weight of the creature impacting you. You cannot include anything the creature is carrying. It was a long arguement that I don't wish to repeat, but the bottom line is, if a creature is carrying something, that weight doesn't apply to any damage a target takes when said creature falls on said target. The creature carrying the extra weight is the one who would have to deal with the damage of impact, not the one you are hitting.
This does not apply if the creature falling is dead.
So, hitting someone with a dead dwarf in a suit of Thaalud Stone Plate is different from hitting someone with a live dwarf in a suit of Thaalud stone plate.
Just another Quirk of the RAW falling rules.