No doubt they are dangerous but they do occur. In some cases, with larger burns, the owner will plan the burn with the local fire department so that they can be on hand to keep things under control. In other cases the owners don't take such precautions and just burn away. I would post some photos of my buddies burn from this summer when he cleared a portion of his property but kids are in all the pictures and I don't want to post them in this discussion.
Out of curiosity, I looked up the regulations for my buddies county and they are pretty relaxed on burning cleared brush/trees:http://www.mdfoothills.com/resident..._department/burning_permits__regulations.html
Acreages outside of Calgary don't have a "local fire department" and houses burn to the ground before anyone can do anything. Aidrie is in the MD of Rockyview and the acreage is close enough to Airdrie. I can see Douglas Garland being crazy enough to openly burn all sorts of things on the property without really caring about the consequences to neighbouring properties.
http://www.rockyview.ca/CountyServices/FireEmergency/FirePermits.aspx