Also, the key phrase you used was "in recipes." Putting a teaspoon of peanut butter in some thai noodles that will be 4 servings is different than making a PB sandwich, which is not on plan.
Actually, a peanut butter sandwich, made with natural peanut butter, bananas, and whole grain/no oil bread is perfectly on plan. The regular plan. As long as your nuts are limited to about 1 oz per day, you are fine, according to both Jeff and Dr. McDougall. It is definitely not on the MWL plan!!
Of course, for many people, peanut butter is highly addictive, and way too calorie dense to eat at all. They cannot eat it in moderation, or their body does not have any tolerance for rich foods. They should stay away from peanut butter all together.
For people who need the extra calories though, a peanut butter sandwich is perfectly acceptable. I ate peanut butter on corn tortillas with a banana to gain weight when i was underweight, and that is perfectly acceptable according to McDougall's article on weight gain.