Unless you are wrong, in which case New York has blown up. That's the point you're missing. You could be right, however, the Doctor, who is usually pretty good about figuring these things out, thinks you are wrong.
The Doctor could've blown up the universe by saving himself using that logic!
Which brings me back to my other point that the Doctor has a certain sense of what a fixed point is. With his own death, he didn't quite realize it at first, but he figured it out (and he figured out that it did not merely involve using the tesselect, but that it required to fake his own death and maintain a lower profile). Here, he's figured out that the fixed point involves Rory and Amy growing old and dying.
Actually, it might be more helpful to think of this as crossing your own time stream rather than changing a fixed point.
My point is more that the authors can easily decide to retrieve Amy and Rory if they want to. There's a very simple out.
If the argument is simply that the writers can cop out, I'm not disagreeing with you. If the argument is that the more logical result of the episode is that this isn't permanent, that's where the disagreement arises. Certainly, if the writers want to bring them back, they are welcome to use any reason they choose (including this one).
Where we differ is that I wouldn't consider it a cop out. It seems entirely consistent with what happened before. Although, having said that, I did think *that* was a cop out!

Mr Awe