The main difference I can find is that there is a significant difference in the amount of people that can read this article. A newspaper can reach hundreds of people and an online article can reach millions of people.
Another difference is that when you are writing online your headline should have discoverable words. If I was writing in a paper I would use something more catchy to catch the reader attention. If I had something catchy on the online article it may not be very easy to find in a search engine. For example the title in an online article was different from the print article that I just read in The Chronicle.
The last difference I am going to talk about is the way you write the article. In a magazine you have to worry about entraining people more. Online you do to a certain extend but not as much. If people are searching for a certain topic odds are they want the facts.
Online and Print writing are both trying to gain and keep an audience.
They both want people to read what they have to say.
They are both a form of journalism.