Whilst we're talking about cooking...are powdered sugar and icing sugar the same thing?
Yes they are. Powdered sugar, icing sugar, and confectioner's sugar are all names for the same thing---extra finely ground fluffy sugar.
Well, they're made of the same molecules, yes. But because one is much more finely granulated than the other, the tastes are slightly different. Like sea salt, cooking salt, kosher salt, etc. They're all salt, but the grain size varies, making them suitable to different things. It affects intensity of taste, sometimes shelf life, speed of dissolution, etc. In general, more finely granulated => greater surface area => stronger taste ('coz more of it touches your tongue at once). This is also why grated cheese tastes better than a block of the same amount and type of cheese. (For those who watch QI, they actually touched on this once: www.youtube.com/watch?v=Uw0KbGi4gH8