Very simple...
You're born with the wrist flexibility
OR
You adapt and acquire it (most folks)
OR
You suck it up and deal with the pain
OR
You play tennis
JP, the open hand position you talk about is very common and accepted.
The best way to develop such flexibility,that I've found, is PNF/isometric stretches followed immediately with loaded stretches in wrist extension. The best is obviously just holding the weight in the racked position. Adjusting your grip width and degree of shoulder rotation will help also.
If you look at 10 different lifters, you may see 10 different approaches just as you'll see 10 different squat techniques.
Bill
P.S. I'm more impressed with the ankle flexibility.