The poll question or answers should be rephrased. "Do you use ocean water or salt mixes such as Instant Ocean?" would have to be answered yes by just about anyone keeping a SW aquarium.
I mix SW myself. Years ago I did collect natural SW a few times. I could do the lugging of that in my youth. I sure can't anymore. I found it to be ok, but that was many years ago. It may be quite a bit different today.
I would say that if you have a good source of natural SW, and you don't mind lugging it and doing some treatment to it, there is no reason no to use it. I would ask the other people that posted to the original post if they have ever used natural sea water? If you have no actual experience with natural SW, it's really not fair to be critical of it, unless your going to back it up with references to people that have used it. Note that there are quite a few aquariums that are on the coast and pump natural SW more or less directly through their system from the local SW.