I'm a programmer. I learned programming over the past 10 years. Take the best lawyer, doctor, or chemist, and I doubt that they can learn to be A player relatively soon (i.e. in 2-5 years). Even if they could learn programming, they would probably not be as good at it as they are at their own original skill. I'm sure it goes the other way round as well.

And after all, why would an A player want to learn a new skill, if they can make a very good living using their present skillset (albeit in a different company)?