Basically what CompVest stated. Each 1911 maker does something different. For example, there are different receivers on 1911s.
This thread would explain quite a bit.
http://forums.1911forum.com/showthread.php?t=246696" onclick="window.open(this.href);return false;
I have a Springfield and a Nighthawk. The Springfield has what they called a classic with A1 relieve cuts while my Nighthawk has the basic cut receiver. Since I'm used to the Springfield and I shoot it more, I favor the classic with A1 relieve cuts receiver than I am on the basic receiver on my Nighthawk. I would go handle as many 1911 brands as you can to see what fits you best.
Basic from the Nighthawk
![Image](http://img300.imageshack.us/img300/3234/img4343ssy1.jpg)
Classic A1 cut from Springfield.
![Image](http://img64.imageshack.us/img64/7176/img1760s8vl.jpg)