At one time, the predators had a hard time finding moths of a color that blended well with foliage. Later, air pollution made a different color a better camouflage. Later still, as pollution receded, the first color again became advantageous. None of this has anything to do with developing new complex systems. The change in moth colors does not involve the development of any new traits, only changes in proportions.
Natural selection works here because there are already functional traits.
The same is true for drug resistance, which is another fine tuning of already developed systems. To make matters worse, drug resistance development requires the killing of millions of organisms just to make one change. Behe states that he can't imagine how some system evolved. However, that doesn't mean that the system couldn't have evolved. A scientist should not give up so easily on natural explanations, especially in light of powerful new technology.