Runehamster: I would disagree. They are very clearly different forms of literacy, but they're inextricably intertwined. Both fluent reading and fluent writing require a deep and sophisticated command of the language you're using, conventions of style and substance, and an ability - innate or acquired - to weave together multiple threads of storytelling or reasoning into a coherent understanding of the entire passage.
I will concede that reading requires a knowledge base from which the reader can extrapolate to gain an understanding, whereas writing requires the writer to engage in conceptualizing ideas, arguments, or stories from his or her knowledge base. This is another similarity, though - both good reading and good writing require the individual to be well read (hence some of the reading problems in America; one must be well read to read well).
If we are speaking of the raw mechanics of writing - grammar, spelling, and structure, then much of this is unnecessary for reading. I too know fairly fluent readers among my students who cannot write. I do not know a single student, out of the two hundred or so I've worked with, who can write well but cannot read well.
I think you'll find that it's normal without being specifically taught otherwise. It's not at all unusual for people to be heads and shoulders ahead in one domain or another of language. My ability to listen in German does not imply that I'm fluent at speaking it, it implies that I've spent a lot of time listening and have gotten good at it. I could quite easily learn to become a master orator in German without any meaningful ability to write, read or listen.
It is unusual for somebody to have an extreme spread, but there are plenty of reasons why one might be a master at writing without being able to read. Or be really good at reading without any meaningful ability to write. I regularly see students lately who are quite good at writing and reading, but can't speak. Or who have rote memorize the grammar rules without knowing how to use them.
The notion that it's somehow unusual is really not one that I can buy into when it's quite common amongst people learning secondary languages.
cjrgreen: If you are going to take the approach of just writing to achieve mastery of writing, you will need either of two things:
A natural gift, such that you can produce fine writing without any knowledge of fine writing; or
The Editor from Hell, who will force you to revise, rework, and delete everything you write until you have learned to write it well.
You can no more learn to write without reading than you can learn to play music without listening. Sure, there's the occasional savant. But that person is never
you.
It's far more common than you give it credit for. Being so educated in a first language is probably not particularly common. But it's quite common for people who are learning secondary languages to be unable to produce speech or writing despite spending large amounts of time reading or listening.
Different domains of languages are utilized in different ways and it's never been particularly well supported the supposition that reading inherently increases writing ability. The way you get better at writing is by writing and optionally by telling stories. Reading and listening might help you identify stories and how others have done it, but choosing one over the other is nonsensical.
Now, if there's a particular style of writing that one is interested in, that's a different matter altogether.