I should have said “written”, then. (GRRM is an infamously slow writer.)
That's the distinction with which everyone is being bogged down.
George R. R. Martin is a storyteller. There's a difference. Stephen King is a writer. Michael Crichton was a writer.
Crichton summed up what it is to be a writer in the most simplistic and eloquent-in-its-brevity language I think I've ever heard: "If you're going to be a writer, then you have to write. You have to wake up every day and sit down and write. Can you imagine if a pilot woke up one morning and said, 'I don't feel like flying the plane today.'"
Basically my point is, just because someone is not adding titles to their bibliography every year or so doesn't mean they're not doing the act of writing every day. In fact, there are many references online to the importance Martin places on writing every day. And in fact, he has published things since his last ASOIAF book.
To try to say "This man is not a writer because he hasn't released the books I want to read" feels kind of silly to me.