I liked what Delirium said. You shoot be able to at least throw and shoot 1 handed crossbows without climb checks.
Have you ever held onto a hand hold and throwing something? You have to realize that a lot of force goes into throwing a weapon. The motion of that force you to have an extremely good hold onto the hand hold you have. Go outside, grab a stick, find a tree, and throw it at the tree as hard as you can. Now realize your body motion in throwing that stick, now think on that. Do you think it would take a climb check to keep a hold of the wall you're holding onto?
Now looks at a crossbow. Have you shot one before? Did you know that a crossbow does have a kick and most crossbows have to be braced on your shoulder with two hands? Well, that doesn't have to work with hand crossbows. Still, trying to aim something while holding onto something that does have a kick, not as much as a regular crossbow, but there is still a kick. Take into the fact that you're likely looking at a combat situation, that would even make it more difficult.
I personally don't see something like a climb check being unreasonable for those situations. More reason for someone that has climb as a good rank being good at doing difficult things with it.
Now onto the topic of edges of a cliff...
This is a problem with the code to be honest. Rooms only have 6 directions you can move, 7/8 if you could count entering and exiting buildings. The issue with creating the edge of a cliff is technically in most cases the transition between two rooms is the cliff. I would have to go into all the details of code and the way rooms work. There is a way to do it, but it would require adding a room to every single edge in the game and then you'd have the problem of making that fit properly and allow for symmetry of the rooms, or you would make every room that is a ledge not automatically make someone fall... but then that would eliminate the risk of falling in the first place from rooms that are meant to have that risk. All in all it is a great idea, but sad that we can't do it due to the limitations of the game. All that work though just so you can shoot off a cliff at someone. Oh, there are rooms in the game though that allow you to look down at another room, but these are rooms made just for the purposes of shooting at something below. The room has to be designed to do it and then there are limitations.
Sorry, I rambled a bit here, but there is a lot of thought that goes into all of this. It's just nice to see code changes happening that are making the game better in the long run.