mete, those who have been there and done that will also tell you that most shots to the gut and chest will usually drop people as well, sooner or later, temporarily or permanently. What those peole who have been there can't tell you, usually, is just exactly why the person went down when shot in the low abdomen. Was it because of getting shot and being in a lot of pain, or is it because they have had a structural collapse of the pelvis due to a break? Lots of people shot in the "pelvis" are either not actually hit in the pelvis, or not hit in an area that is going to cause a structural collapse.
As noted by armedandsafe, the shots need to be fairly precise in order to get the desired result. Given that most shooters have such a poor understanding of anatomy and biomechanics, for them to effect a pelvic stop shot that 'breaks' the pelvis is going to be more about randon chance than skill and marksmanship. On top of that, the vast majority of the pelvis can suffer damage without causing locomoter breakdown.
On a clothed person, male or female, do you know what landmarks you need to be able to identify in order to hit the precise areas in order to cause a pelvic break that will preclude locomotion? Probably not.
When I took my first handgun defense class, I was instructed where to shoot so that I would hit and break the pelvis. The moron instructor provided incorrect information. I have seen this sort of information repeated by other instructors and I had to upgrade my assessment from moron to ignorant. Simply put, most don't have a clear enough understanding of the topic to actually be able to explain properly where to shoot and how the shot will affect the pelvis.
I was told to reach down and feel the bone underneath my pants front pockets. I was told that what I was feeling was the pelvis and that if I shot it, it would break and the person would collapse to the ground, unable to walk. What the instructors were having us locate was the pelvis, the iliac blade, actually. This is the largest portion of the pelvis, but one that holds the least amount of locomotor stress. Its big job is in acting like a bowl to support the lower muscles and organs. Unless it snaps in half or is damaged at the socket, this bone can take a lot of abuse without causing locomotor breakdown. You can puncture it, break of chunks (such as those areas you feel under your pants front pockets) and the person still be fully capable of locomotion. It would be painful, but so too would any ballistic wound.
Take this little anatomy lesson a little further. When old people fall and break their hips, do you know what has actually happened? Next time you get gun instuction for shooting the pelvis, ask your instructor to explain to you about what happens when old folks fall and break their hips. See if he gets the answer right. If he doesn't, don't put too much stock in his instruction on ballistically breaking the pelvis until you can verify his information.
What does happen? First, the sequence of events is wrong for most cases. Usually old folks break their hip and fall. It is associated most with older people due to osteoporosis, bone loss. Okay, so what is actually breaking? It will usually be one or both of two areas. The first is the breaking of the femoral neck, separating the head of the femor inside of the acetabulum (socket) from the shaft of the femur. The other break is going to be the acetabulum, either where the head of the femur punches through or where the side of the socket breaks free.
Pelvic shots can be good, but don't count on being able to hit the pelvis in such a way so as to cause the proverbial pelvic break that is so commonly mentioned in gun lore.