In my experience (and this is at a "top" school/program), this has not been the case at all. In fact, a lot of the types that already had prior experience seemed to struggle when it came to more difficult or theoretical/mathematically rigorous classes (e.g. Algorithms & data structures etc.). I suspect that a lot of those who had already programmed did a lot of little personal projects or hacks. Maybe they learned some different languages, played around on the command line, generally dabbled in different areas of CS and software, etc. But I think the kind of skills gained from doing these sorts of things are mostly trivial. The types of problems solved in most typical apps and websites are not that difficult technically. You learn about a lot of the difficult problems in software and computability through CS material. And the other difficult problems are engineering ones - things like necessarily complex systems with lots dependencies, large-scale or scalable systems, software with high technical demands, comprehensive testing etc. etc. But that kind of thing is learned on the job, or at least in some kind of capable team working on an important project. Not by writing little scripts or apps on your own. Learning how to write readable, modularized code can be naturally (and fairly quickly) learned in intro classes if you are mindful and dedicated to improving.
However, this is just my own experience and observations. And there is no doubt that there are plenty of people out there who started at a young age, and are also superb at computer science and/or are fantastic engineers. But I don't think that in itself is a great predictor of someone's capability.
Clarification: I'm not saying that it's a necessary requirement; I'm just saying that I certainly see a correlation.
By the way, this has been brought up as the reason for the dropoff in the women who enter CS curricula in college. Ever since home PC's became affordable, freshman CS classes have basically assumed prior (and thorough) computer experience, and many women who might otherwise become good programmers, for whatever reason (society influence, etc.) have had waaaay less hands-on time with computers than boys, when they become freshmen.
That said, I have met some excellent programmers who started out doing something that is superficially completely different (musicians, for example).
I imagine that it depends on the school but there's probably some truth to that. I've taken a couple of "Intro to Programming" type classes from top schools. I found the material quite manageable--but then I have a moderate amount of programming experience even though I don't do it for a living. I'm pretty sure that if this were the first time I saw a computer command line or wrote code, I'd have been lost. Freshman physics at those schools may be challenging but it doesn't assume a whole lot of prior exposure (other than an appropriate level of math).
In 2010? This article is supposed to be about US, not a third-world country, right?
I don't for a minute believe it is necessary to have been coding since you were 12 in order to do most jobs in Silicon Valley. But if companies decide to discount people because of it, then you will absolutely filter out people who come from lower economic backgrounds.
This is a great example of institutional racism.
All of it ends up affecting their hireability.
And yes, we offer extremely competitive salaries not typical of the east coast.