from spwenger's links...
Dr. Williams specifies that it is the lateral pelvis that should be targeted, particularly with a handgun. The lateral pelvis is the area between the edge of the sacrum (the set of fused spinal vertebrae that form the central, rear portion of the pelvic frame) and the hip joint. This area can be envisioned as a triangle which encloses the bone structure that is most vulnerable to damage from a handgun bullet, compromising the assailant's ability to remain standing or mobile.
The "lateral pelvis?" He is describing the ilium. It is the area most vulnerable to damage because it is the largest bone of the pelvic girdle. It is also the bone that can take the most damage without failing. It is so large because it is the major point of attachment for the abdominal connective tissues and forms a partial protective basin around the lower organs.
Relatively speaking, you would do a lot more damage with a single shot to the pubic bones, only most people would be clueless as to where to shoot and both are very small compared to the ilium. The same would hold for the ishium, larger than the pubis, but much smaller than the ilium.
I have yet to find any data to suggest that a shot in the pelvic area with a handgun is any more or any less effective than the 'belly button' shots described on your page (ala Farnam). The belly button aim point gives you a lot more room for error while still hitting your target.
As best as I can tell, there is no study on pelvic shots that compares and contrasts gunshot damage to pelvises, especially not any handgun data. Yes, Ayoob cites a real case where a person was shot, hit in the pelvis, went down. Given a bit of time, I can find the articles on appendicular soft tissue (non-bone involvement) gunshot wounds where people went down.
Fackler specifically refers to the pelvic shot concept as a fallacy, and it may be in terms of the perceived results people expect, just like the head shots you mention on your web site that don't do a lot of good because they miss the CNS.
However, if you have some data you are holding back that will show information to the contrary, I would like to read all of it.