Statements like this can frustrate both sides of the debate. Words like "theft" really consist of a cluster of related meanings. Copyright infringement probably satisfies some of them, but not others. I think your case would be better made by stating more directly what you mean. For example: "piracy does not take away someone else's material goods and so is not as immoral as Biden's comparison with smash-and-grab theft would imply."
This reminds me of an awesome article that discusses the debate about whether or not "obsesity is a disease" http://lesswrong.com/lw/2as/diseased_thinking_dissolving_que...