Dear Mike,
Interesting and plausible theory, but certainly not the answer for all causes either.
I never had BPH, and even with my urethral stricture problems have always successfully emptied my bladder with each void. I tend to go freqeuntly, so holding it a long time isn't the issue. I never smoked although my father smoked heavily when I was a child. My father also had a benign bladder polyp, but before we jump on heredity or second hand smoke, my identical twin who grew up in the same smoky house has not had bladder cancer, thank God. I do not work with chemicals. My twin teaches chemistry and did smoke when he was younger.
As much as we know about disease, as a physician I realize that once we get past what we do know, we still can't explain the variability of how disease presents and why patient A fares well, patient B does poorly, and patient C doesn't get what A & B had.