In those twenty years, the magazine has covered books fairly well, but has showed authors on the cover rarely. (They have run dozens if not hundreds of cover stories about movies based on books, but those show actors, not authors.)
I can recall only two cover stories with the author himself in the spotlight (from 1994 and 2002, respectively):
The current issue, however, pulls a neat new trick. I believe it is the first time the cover has depicted not an author but a book itself:
I realize this is a milestone only in my narrow little pop culture realm, but it's still a nice thumb's-up for the publishing industry.
Now let's see if an author of books for children will ever make the cover...
Don't snicker. Kid-friendly properties routinely do. Eventually one of the creators may as well. As long as s/he has a big personality. And, of course, a purty face. Thinking back, it's unjust that none of the mag's many Harry Potter stories devoted the cover to J.K. Rowling.
In this issue, editor Jess Cagle writes "Why aren't there more book-themed covers on EW? The answer is obvious: If you've got an overall audience of nearly 18 million (including our magazine and website), movies and television are the fastest way to the greatest number of hearts."