I just read Kevin's post and I read Sam's before, so I thought I should go ahead and add what I know about language to answer a couple of these questions.
All humans are biologically built for language. Although no one actually "leaves the womb with the skill of words", everyone who is exposed to language learns it rapidly and completely without any effort. This included vocabulary, sentence structure, and grammar. There are two centers in the brain, called Wernicke's area and Broca's area, which are believed to be mostly responsible for language. Damage to one of these areas can cause damage with both how people write and how they speak. Written language and spoken language are closely related in that we have to get the words we use, no matter what the medium, from our mental lexicon. Writing, though, is unlike spoken or signed language in that it is not learned without effort. We have to work pretty hard (some harder than others) to even learn how to write the alphabet. The idea, however, that some people are inherently more talented with certain things has yet to be explained by science. Personality and talents have not been identified anywhere in the brain or elsewhere...yet.
If you're interested in any of that, you might consider taking the class Language and the Brain. I think it's CSD/LIN 350. Also, yesterday in my German class one of my classmates said that he read somewhere recently that reading and writing are not natural to humans, and this is evidenced in part by the fact that so many people are dyslexic. Interesting.