I've wondered that for a few years now.I wonder if the cigarette companies have added a chemical to enhance the addition of nicotine or was addictive on it own to the cigarettes that is not in the pipe tobacco.
I can enjoy a bowl of Bold Kentucky without being bowled over, so I clearly have a tolerance for nicotine, but I can also put the briar down for a few days or weeks if I have a cold or something and not experience any symptoms of withdrawal.