I take it you've never promised something that you've been unable to follow through with. "Social contract" is a very nice idea -- and dude, do I ever want to read that next book -- but the reality is that people are frail.
I don't think "promise" is the best word here.
The flaw I see in that reasoning is that most cases money isn't changing hands.
If you go into work, and you promise that you'll have X done by Y, then at Y shrug and say "oops," you
might get away with that once. However, you're being paid to do something, and it's not unjustified to expect a return on that expense. Now, obviously writing is a little different, but not exceptionally so that it invalidates the thought exercise. Perhaps a better example might be an investor and a company; the investor needs customers to make money, and the company needs to produce.
This brings me to where I think the
real problem is - the publishers and editors. They absolutely need to put their foot down with him. In fact, I think it's the exact same problem that was had with Robert Jordan. I'm not saying all creativity needs this - in fact, I think most authors do fine without it. That's reason enough for me to say that they need to step in. Obviously at some point there's been a breakdown in the publisher-editor-author process at the author end. That's
why there are publishers and editors.
I can understand and sympathize with GRRM's frustration with his fans. I think a lot of fans are over the top, criticizing him as if he's not allowed to have a life outside of writing. It reminds me of
Misery, and not in a good way. However, I don't think their behavior excuses him from all criticism about the timetable of his writing.