O-trap,
Without definitive numbers, it's impossible to argue if this helps or doesn't. I'd be willing to bet that the kids that you're referencing fall into a minority.
I know from personal experience, that every decision I made needed to be thought out throughly or else there were going to be consequences. With that said, I can literally count on one hand the number of times I got beat. For us, it was more about the idea than the actual act. I can also list the families in the neighborhood that beat their children (I'm not talking about child abuse) and those children grew up to be upstanding citizens, just like I can name the families that didn't give two shits about their children and those are the kids that have been in and out of prison for the past 20 years.
I don't condone beatings, I think it should always be the very last option as a punishment, but I also don't think that it should be vilified.
As far as beating girls, I do think that after a certain age it does have the opposite effect. Maybe it's my sexist mentality, but I believe that after a certain age girls can be more easily disciplined psychologically than physically! (I'm not quite sure if I'm stating that correctly)

Oh, I also know parents that say they beat their kids, and from time to time my actually backhand them, but for the most part do not implement any kind of discipline in the household!

I'm not a child psychologist either, but only know what I've witnessed growing up in that type of household and community.