That greatliteraryworks article is interesting.

Most of what we regard as great literature was written for money. Shakespaere, like someone mentioned. Eugene O'Neill comes to mind. All stage plays are written with production in mind. So writing for money doesn't rule out a work being great.

As far as deeper meaning being the mark of great literature, who determines what deeper meaning is? I've always liked sci-fi because it can examine things like mixed marriages in a roundabout way. Instead of a negroid/caucasoid marriage, you can have a Reptilian/Human marriage and still deliver a tolerance message. You can bury messages in sci-fi. Comedy, too. Court jesters can get away with kidding a tyrant while a straight-faced critic would be executed.