"In contrast, Sopko et al. (1985) in a twelve-week study, with obese men, reported that when the negative energy balance created by diet only and exercise only are equal, the two treatments produce similar results. The participants in the diet only group (n=10) experienced a weight loss of 6.1kg by restricting their caloric intake 500 kcal/day. The exercise only group (n=6) lost 6.2 kg by performing a treadmill walking program in which they expended 500 kcal/day. The men in the diet only group went from a body fat of 31.4% to 25%, where as the exercise only group went from 26.7% to 19%"

From reading this, it seem like many studies didn't attempt to make calorie deficit equal.