I think it's a disparity in the way people think. I tend to believe that intellectual property cannot be "stolen," for much the same reason orathaic is posting. It's an idea, a chain of ones and zeros. Making a copy of such a thing in no way deprives the previous owner of that thing.
KC, and the US government, don't see it that way. Intellectual property has value, and to copy such a thing without compensating the owner for his property is unlawful and wrong. Even though you aren't shorting the owner any physical item, you are effectively depriving him of the value of what he owns, and his right to profit from it.
So is it "stealing?" That's semantics, if you ask me. The concept of theft has been around a very long time, and is usually associated in our minds with taking of a physical object. The idea of digital theft is much newer. If you believe that people have a right to retain intellectual property, then you must view digital piracy as theft. If you think that concepts, ideas, and information are and should be free, then I think you're off the hook, according to your own morality.