Take a look at this image:
How many corkscrews is that? The obvious answer is "one", because each of the four and one-half 360° turns is attached to the next, and you can only open one wine bottle at a time with it.
So why would a roller coaster corkscrew be defined any other way? Vortex has one corkscrew that makes two 360° turns. It's most certainly not two corkscrews, because if it is, then the image above shows four and a half corkscrews, meaning that you could use the tool depicted to open four wine bottles simultaneously, and that's preposterous.
Edited by jcgoble3, 24 June 2013 - 09:31 PM.