Creativity trumps skill…but skill is what gets you where you want to go.
Writing sales and marketing materials is a specific kind of writing. Its goal is persuasion (to appeal to the part of the brain where buying decisions are made) and to promote.
Newsletters and sales letters are essentially about building relationship and delivering information.
Books and articles are usually intended to educate, tell a story and build pathos.
Web Writing combines all these elements while incorporating elements specific to the internet environment. Unless the goal of the site is academic, web writing is short, concise, compelling and keyword rich.