How I see it...
Motivation plays a huge part in becoming adept at any skill or discipline.
The seeds of motivation are usually planted in very early childhood, either by the parent, child, or peers such as teachers.
The child then discovers that by learning, goals can be achieved.
Whether it be a child who becomes motivated at sport, academics, music or magic—I still think that the word 'Skill' is defined exactly correctly by dictionaries—it's something you acquire by learning.
Sure, genetically we're all different. But skill isn't stored in our genes. Some say that parenthood is a skill which is in our DNA, but in my opinion, it's something we subconsciously recognise throughout life as 'the right way to be' and just act accordingly when the time comes.
This thread may go the way of the 'creative' thread (Mr Jamez remembers this one well...

). But I think to expect that we are born magically talented is little more than an illusion.
As Craig says, some people are born with different aptitudes: a child born with a developed physique could probably become an athlete, versus a child born with an exceptional mind could become a scientist.
But I still believe that the motivational aspect accounts for what PATH these people take. I am not sure that someone born with the genetic makeup of a master athlete will ALWAYS end up that way, but because they excel at sport during schooling or growing up, perhaps they realise that this is what they are good at, ergo, enjoy it, and become motivated.
As humans, we have choices.
A racehorse bred for it's pedigreed parenting has been 'crafted' by careful selection of mother and father. This gives that horse the best possible base for training it to become a winner.
And it USUALLY follows that if a child is born into a family of well educated doctors, the child will be motivated by the success and nurturing of their parents, and get educated—possibly to become a doctor.
Wheras, it USUALLY follows that a child born into an uneducated, poverty stricken family, the child will lack motivation to become anything more.
I am not stereotyping or pigeonholing here intentionally... but I think it's a fair indication that we simply become what we WANT to be.
As with anything, becoming skilled at magic requires motivation, knowledge and dedication.
We're not 'born to perform'. I believe we are somehow moulded that way during our upbringing.