The prostate hypertrophies with age regardless of nutritional input.. and thus has a high rate of developing cancer. I'd be wary of saying anything has a correlation or causation with prostate problems.
Anyway, near the end they linked dairy PROTEIN was the probable correlation:
Analysis revealed that a high diary protein intake was associated with an increased risk of prostate cancer, at a hazard ratio of 1.22 for the top versus the bottom quintile of intake. After taking into account measurement error, the team found that an increase in dairy protein consumption of approximately 35 mg/day was associated with a 35% increase in the risk of prostate cancer.
Guess that doesn't speak well for whey or casein, heh. Shrug.
edit: poor grammar