Content writing is different from other forms of non-fiction writing and thus requires a unique skill set. Copy writers are able to write coherent, well structured, and concise articles with a strong title.
Content writing typically refers to the kind of writing you'll find on web pages. A copywriter is usually responsible for writing short, well structured, and researched articles on any given number of topics. Good web content writing needs to be able to quickly grab a reader's attention and the themes within the text must be easily identifiable. Your standard web surfer tends to peruse what s/he is reading, quickly scanning a passage for key information.
As such, content writing, or copy writing as it is often called, is different from other types of writing. Copy writers are usually skilled with language; they have excellent grammar, an ability to efficiently extrapolate key concepts, and an ability to synthesize these concepts into their writing. Copywriting should be relatively informal. Although it is grammatically sound and well structured, it is acceptable to speak directly to and with your audience. In addition, the writing needs to be incredibly concise. You have to write short, direct paragraphs. Remember, web readers tend to skim so you need to hit them with the point right away.
The mark of an excellent copy writer is their ability to write a dynamite title. A copywriter, and especially an advertising copywriter, almost needs to tell a story in their title. Ok, well not quite a story but a number of elements need to be conveyed. First of all, it has to "pop". A reader needs to glance at the title and be stopped in their tracks. A good title also has to summarize the article. The reader has to be able to immediately understand what the article is going to be about. Finally, key words are extremely important. Content writing is directed at the web and in a web based world, most sites are found through key word searches. So a good title should increase the chances that the article is going to be found by virtue of the key word search.
Probably the primary difference between content writing and other forms of non-fiction, like journalism, is brevity. Content writing must get to the point immediately, key concepts need to be easily identifiable, and the passage must be easy to read.