I believe the problem is that people AREN'T using the smaller quantities. They are using the same size of joint, for example. But getting a lot more THC than they might realize.
That's really quite silly. Pot smokers know how much they are smoking. First, pot smokers are derided as being dope obsessed pot smokers who grow weed and send the pictures to High Times. Now, we here that they really don't know how heavy of a hit they git. That's just silly.