Are there any rules for writers?

I was at the bookstore yesterday, in a quest to find some reference material for a story. I don't normally go to the bookstore that often, as Wikipedia offers me the highest quality, accuracy and unbiased research material (The Encyclopedia Britannica are rolling in their storage boxes) found on teh internets. Of course, I didn't find the necessary reference material. It would've been under Biography, but there wasn't an actual biography section. There were a few biographies thrown into the American history section, which was surprisingly large, dwarfing the rest of History. No wonder the whole of Europe hates us.

I digress. What I did find was a rather large section devoted to the rules for writing. I wonder if there was a book on writing blogs? It was probably next to James Joyce's guide for writing stream of conscious. He would have had an excellent blog. Back on track. Writing is an art-form. While there are certainly better ways of doing things, and definite guidelines to follow if you desire to be published, I didn't actually think there were rules (my English teachers are rolling around in their storage boxes too). If so, what are these 'rules'?

Has language de-evolved, thanks to Twitters, textings and blogs like mine, to the point that grammar, sentence structure and spelling are not as important to literature, so long as the story is good, readable and makes sense?