Maybe I am mistaken, but I thought that the spider crab was more commonly known as the Alaskan King Crab. The name change has everything to do with marketing. Eating a kind crab sounds a lot more appetizing that eating a spider crab.
This practice is actually more common than you would expect. I know that Chilean Sea Bass used to have a much less appetizing name, something about bottom sucking if I recall. They just slap a new name on it and suddenly the exact same thing is fit for a menu spot on some of the fanciest restaurants.