Lance pretty much touched on everything.
Companies pick the shape they want. Depending on the manufacturer, there are tons of options on what you can tweak. I personally wanted a pretty equal length nose and tail, with both having a full roundness to them, and Pennswood was able to do that.
And like Lance said, most manufacturers press multiple boards at one time. Depending on where that particular board was in the stack being pressed, the concave will differ from what deck to the next.
PS Stix boards are pretty consistent from what I know. Solid molds, and CNC cuts. I'm sure Habitat picks their shapes, but I could be wrong.