This column on getting news on the Web has a fantastic rundown of what copy editors do. Ahem.
Getting a story online is a major technical achievement under normal conditions. The writer has to gather information, write the story in a publishing template, do headlines; a copy editor goes over it all looking for misplaced commas and nasty typos that creep in; a Web producer develops the look for the story. It has to be co-ordinated so the story is posted with all of its elements in place. It's like publishing a newspaper but much faster, with minute-to-minute deadlines.