I'll throw in my .02 on this, Doc.
In most cases, when you castrate a male or spay a female you are trying to get rid of unwanted behavior and POSSIBLE future health problems. If you are going to render a male neutered, you may as well take away the chance of them getting prostrate problems and testicular cancer. If you are going to spay a female, you may as well take away the chance of them getting mammary or ovarian cancer and Pyometra (sp?), an infected uterus that can kill quite quickly. Plus you are elimating bitches from coming into heat, as opposed to if they had a hysterectomy like a human, uh, woman /forums/images/graemlins/grin.gif.
Also, the operations the vet does in spaying and neutering are MUCH simpler than going in, breaking apart muscle and snipping or tieing tubes.
Like I mentioned in an earlier post, unless you REALLY work your dog or compete with him on a professional level, most people aren't going to notice too much of a change if any. Cowboy Doc obviously works his dogs in an extreme manner and I have no doubt he sees change.
That's how I see it anyway.