According to Dr. Katie Bowman, an expert in biomechanics, (http://mamasweat.blogspot.com/2010/05/pelvic-floor-party-kegels-are-not.html) urinary incontinence isn't necessarily caused by pregnancy even though pregnancy increases strain on the bladder.
The weakening in that area seems to affect both women and men with age. She explains that pelvic floor weakening occurs from a slack in the muscles due to the sacrum moving anterior or into the bowel.
The muscle should be supple like a trampoline. If you exercise your pubococcygeous muscle (Kegel) without compensating in your glutes, you can pull the sacrum even further forward and worsen the problem.
The solution? Evenly align the sacrum by toning both the anterior and posterior sides of your pelvic floor muscles. Kegel regularly, but SQUAT often.