The largest jump in the world was not counted because there were not enough spectators.
As for them being dangourus, they knock down, and I think the rider wouldn't do it if they thought the horse was not up to par.
Whoa I only jumped 5ft recently and at a 6 bar comp I cleared 1.82m on my old EFA horse, he was a freak of nature though! Completely nuts but he could jump the moon! He is now happily retired in my back paddock living out the rest of his days!
I was at the washington international horse show this past october and they did puissance and the jump went up to 7 foot 8 inches. I think it was too much of a push for the horse. He could jump it, but people push these animals too much on some things. Heres the video I took of it. Its far away and its facing the back of the jump.