There is only one variable being discussed when we're discussing that variable. This is not a discussion on creating a highly-predictive model, but rather discussing trends in how higher scoring players tend to succeed more...
Why do people keep on acting like I am singularly focused on scoring? Am I not communicating well? (Totally possible... I'm a very meh writer)
and
Plus multiple other comments with the key words like "trend".
I know these other variables exist and matter. I've never once took the stance that these numbers are saying everything. I'm just adding one more layer of information.
This all came about when I said: Hey, Slater scored at a higher rate and was a highly valued and projected prospect (1st rounder). He was valued highly by scouts. Was a leader on a team. And was successful in carving out a long career as a NHL player but was never a plus player. So, be careful in getting overly excited on players. **** happens.
That's it. Caveats added on doesn't change that point.
To answer some of your other questions, NHLEs seem to point out that the model is mostly linear regression is most appropriate, although Volman has found that there is a limit and a tail off. The probability curve is likely skewed. Anyways, I linked in my article to a good article though that discusses this further.
Edit
As a little add on I think this is a neat aspect to look at it:
http://assets.sbnation.com/assets/666667/nhlchart_medium.JPG