"It's not that 37signals writes software for themselves and no one else: they write it for themselves and people like them."

I don't think that's true. I think the correct statement is:

"It's not that 37signals writes software for themselves and no one else: they write it for themselves and people WHO HAPPEN TO BE like them."

There's a difference.

I think you are utterly misunderstanding Norman. He's not saying you're dumb for using those tools-- he's saying that 37s is dumb for not trying to understand and adapt to their customers. (Incidentally, is exactly what Apple is doing with the SDK and Enterprise features)

Because of their arrogance, they are leaving money, customers, and customer happiness "on the table". No harm in that-- they're rich and have enough happy customers...