Do you happen to have any evidence for #2? I work at one of those companies and picked up coding in college, and so did at least a few of my coworkers. I really have no idea how common it is and would love to know.
#2 I have no evidence that time spent learning and practicing a particular discipline influences skill level, but I am guessing that there is a correlation :). For majority of top schools aside from Barkley it is not a prerequisite to enter into CS program. From people I personally know which is not a representative sample I'd say 50/50 but it skewed by good number of them having Stats./Math as original major and then CS Masters or Ph.D.