I wonder why Gentle Giant is on that list... Even though just a 10% have voted for them as the band that should not be here, just the fact they appear on that list, makes me think that this could be a joke...
I know Queen and Deep Purple are not 100% progressive. The first one, although being a hard rock band, were influenced by prog and the second one developed the prog style on their early years, before taking a different direction...
I think most people voted for Nightwish because the band is too over-rated and because of all their commercial success in Europe. Besides, their sound is more power metal than any other thing, and cannot be compared with such classics as Deep Purple and Queen... So Nightwish becomes the scapegoat and carries all the burden...