It doesn't seem possible to me that cannabis contains any nicotine let alone 600 times more nicotine than tobacco.

Here is my reasoning, lets say the average cigarette contains 1mg of nicotine (some brands have more, some less) if marijuana did in fact have 600 times that amount it would mean the equivalent weighing joint would contain 600mg of nicotine. This is 10 times the human lethal dose. (60mg)