Good picture diagram to explain: https://anatomy.elpaso.ttuhsc.edu/modules/pelvic_autonomic_module/Files/pelvic_page12p.jpg

Penile urethra doesn't pass through the prostate. Prostatic urethra does. Dome of bladder is not near the prostate. Parasympathetic nerves are close to the prostate, hence more likely to be damaged during radical prostactectomy.