Because it is not a spiral. I just looked it up and, like a lot of words
that are commonly misused, the definition of spiral has been *******ized. In
my line of work, where geometric correctness is important, no one would ever
interchange the terms.

"Don" wrote in message
et...
Why?

"CW" wrote in message
...
It's not named correctly either.

"Don" wrote in message
nk.net...
A spiral stair is not shaped like a cone.