Parent was referring to patents, so I assumed you were too. Of course physical property makes more sense as a analogue for copyright law. But it is still flawed; in most cases involving copyright infringement (example: downloading a song) you have not harmed the copyright holder in any measurable way, whereas with theft they have lost what you have gained. See this [slashdot.org] previous post for clarification.
There are many facets innate to copyright that do not allow it to neatly fit within a property rights context (though it can certainly be shoe-horned into property rights if that sort of treatment reflects politicians' desires).