Web design is strongly connected to print publications, but allows designers to add:

Interactivity

Explanation:

In design term, interactivity refers to the way the design could response to the input given by the users.

Compared to hard copy, we can say that web design allow much more interactivity.

For example:

On a news site, the designer could design the page to place written articles just like hard copies. But the designer could add some sort of link that can directly show a video form of the news that customers is reading. This type of thing is inachievable in normal newspaper.