My threads 
vermonter - There is no difference between "bulky" muscle and "lean" muscle.
Kettlebells have both a greater technical requirement and uneven leverages that will make them inferior for building muscle over a more balanced implement, particularly in the torso of the body, although an argument could be made for increasing benefits to the muscles as they insert closer to the hand (per pound of weight lifted, that is).
Cotter does a considerable amount of non-kettlebell work, and on his most recent DVD set states that for the development of strength it is required that you perform bar lifts to supplement your kettlebell work.
Great post!
The main benefit of kettlebells versus other implements is the efficiency of the workout. They grant the widest range of fitness benefits, using the least weight relative to bodyweight, in the least amount of time. For overall strength though, there isn't going to be a heavy enough kettlebell for anyone in decent shape not to be able to deadlift or squat it - though they may have trouble cleaning it. Pretty much all kettlebell instructors and practitioners will still have at least one barbell training session a week.