It does fit the S&W #637 but for the S&W 60 we would need to add about 1/2" for the safety strap.
Here is a picture of the back which will explain the lower strap.
The shape of the holster is because it fits the gun. I'm not sure what else to tell you about the shape.
One thing I like about this holster is that it can be slipped on and off without unfastening the belt and that is very convenient.