You quoted an internet article about cancer when the original topic was your book discussing damage done to the lungs
The problem is that they don't define "regular use". A joint a day? Three joints? As many joints as ciggs? It is a lame premise.
That was the stat that I had learned also. It's a little tricky though. 1 joint = the same amount of residue as 6 cigs. The not often noted fact though is, like many people have noted in this thread already, that the residue from weed has shown to actually protect against lung cancer, not cause it. THC is also a bronchodilator*, so it gets cleared away easier. *Dilates the tubes in our lungs, what people take for asthma.