I agree, it is perhaps possible for some organisms to exist completely without water. The reason it is said that water is necessary for life is it's role as a solvent for many chemicals that allow lots of crucial reactions to take place in solution. As far as I am aware there is no other liquid that can act universally as a solvent to so many important substances. In my opinion this is why water is one of the first requirements people look for when searching for extra-terrestrial life.
On the other hand, the possibilities with regards to space are endless! Perhaps life exists in a form that we simply cannot conceive.