In a recent post on his blog, agent Nathan Bransford compared writing and storytelling, inspired by people who criticize best sellers for their poor writing. I won't repeat what he said (see the link in the first sentence to read it yourself), but his basic premise is that there is writing (mechanics, grammar, punctuation, sentence structure, etc.) and there is storytelling, and even if some find the writing of a popular book to be subpar, something in a best seller grabs bunches of readers. That something is the storytelling.
I'll admit there are times when I raise my high-brow literary nose at the writing in some books, but I have to agree with Nathan. His post got me thinking about why a good story trumps perfect writing mechanics.
The obvious reason is that your average reader goes to a book to be entertained. This reader might or might not be intimately familiar with the rules of "good" writing, but for a large number of readers, that doesn't matter, as long as the mechanics are not so awful that the book can't be read.
As writers, we're much more aware of the rules, so much so that we get caught up in them. When we're writing and revising, we're deep in the world of mechanics. We care deeply about how words fit together, how sentences are put together, how many adjectives and adverbs we have on a page, rhythm--all that stuff. As we should be. But if we do our job well, all of that is transparent to most readers. In fact, even if we mess some of it up, it's going to be transparent to readers who aren't as familiar with the minutia and just want to be entertained.
Of course, if we can't put a legible sentence together, we're not going to write a good story, so good mechanics are important. But if the reader is engrossed in a ripping yarn, they'll forgive some writing issues. This is especially true of younger readers, many of whom really just want a good plot with interesting characters. There are, of course, young readers who really care about the language and want books that are beautifully written as well as great stories, but few readers will stick with a dull story just because the writing is great. Some of us will, because we love language and admire the writer's abilities.
When it comes down to it, though, we'll forgive an average writer who is an excellent storyteller, but we'll have trouble sticking with a book full of lovely language that doesn't say much to us.
As writers, it's our job to learn all aspects of writing books that people want to read. That includes both the mechanics of sentence structure and the mechanics of storytelling. The structure of a good story (plot, scene structure, characters, dialogue, and all the rest) are enhanced by good sentence structure, strong nouns and verbs, rhythmic sentences, interesting word choices, good grammar, and the other things we learned in our comp classes.
Your chances of being published increase when you have the complete tools, not just some of them. When it comes down to it, though, reading is usally a form of entertainment, and entertainment equals story.