My 2 cents...
It seems you're calling "articles" and "web copy" by the same name. They are two different animals.
Articles (examples here
) are informative and found usually in magazines, ezines, blogs and forums, etc. They are most often not designed to be direct
sales tools (with the exception of your small bio at the very end of the article).
Website copy, on the other hand, is designed to directly sell and/or otherwise persuade the visitor to take some sort of action. (Example of web copy
Writing something - as Kirk pointed out - is the original creation of the text whether it be an article, web copy or anything else that is written.
RE-writing is doing it again. In fact "re" anything is doing it again. There are lots of reasons to re-write something. To edit it for better flow. To include new information that wasn't there when you originally wrote it. To create a version for online use that won't trigger a duplicate content filter and dozens more.