Shakespeare - not so clever now?

While reading Hamlet, I was struck by how many of the phrases he uses we use today. In fact there's whole websites devoted to this subject. Here's one, where they say, "Many quotes from the works of William Shakespeare have entered into common usage".

But what if they didn't? What if Shakespeare's plays were actually full of cliches he'd ripped off from common usage of the day, ha ha! How would we know?

So the moral could be, fill your writing with cliches from 2009 and in only a few centuries you too could be the source of quotes! Except sadly it wouldn't work, because everything, even the most mundane, is recorded in writing these days, unlike in Shakespeare's. Foiled!