One of the key points that come up all the time with these 'physical goods vs. digital goods' discussions is that the latter can be distributed endlessly. Why

One of the key points that come up all the time with these 'physical goods vs. digital goods' discussions is that the latter can be distributed endlessly. Why is there no way for me to give something I bought to my friend, digital or not? We have a digital currency now that claims that I cannot both send you money and keep it at the same time. Why isn't this possible with my mp3s, ebooks and movies?