I just use my blender to make smoothies, and it works absolutely fine. I can't see a difference either, and I don't think I would shell out for a smoothie maker whilst I can use my blender.
All this talk of smoothies has made me want to drink one! I wonder if there are any strawberries in thef fridge...
I just use my blender also. Don't see a difference between the 2 machines. I don't like the spouts on the other machines, I think they would be hard to keep clean.
I wouldn't bother personally if I already had the blender. There isn't much room in our kitchen for new appliances, so I think I would just make do with what I already had.