It seems to me, as an outsider, that Joel's reason for avoiding a rewrite at any cost is because so many rewrites have failed. Perhaps it's better to prefer steady, step-by-step progress over a giant leap that might be a leap backward in the end. What is often forgotten in these discussions is that, because Fog Creek had talented programmers, writing Thistle and eventually Wasabi was just another series of steps on the road, not a giant leap as a rewrite would be.
