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 ******* 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.