i too wonder at this phenomenon, however as i smoke more i think i am starting to see what is meant by strength. i believe that what you are percieving is not that the cigar is mild in body, but smooth in flavor rather than spicy in flavor. i think i started to pick this up after smoking some full bodied cigars (my favorites are maduros) and having the same feeling that they were very smokable. then later i smoked so more full's but ones that where also spicy (CAO brazilia) they had the same quantifiable amount of flavor but the picy ones were more harsh so i percieved them as more full bodied.

P.S. i am also a n00b so this could be and in all likelihood is 100% wrong but this is the way i worked it out in my head. hope this helps.

J