It’s not any different. You are allowed to make copies from one media to another.
Here’s why:
Copyright law isn’t about physical copies. Copyright law is about this mysterious idea of intellectual property. Only in the last few decades has it become feasible for people to make copies of works easily, and the law has not really caught up, in part because everyone is scrambling to make sure that their preferred solution is the one congress and the courts adopt.
It’s easier to think of copyright as a license to use the information comprising the work, and modern law has been slowly moving toward this interpretation.
The real problem is defining the word “copy”. The general meaning is to make another instance of the same information, which is the definition we use in day-to-day life. But the word copy has a different meaning in the law. A copy for the purposes of copyright law needs to meet several different criteria. One is the old “fixed in a tangible medium” standard, but there is another semi-unwritten assumption that the copy is a purposeful one. Copying a program into RAM so you can run it is not a copy in the legal sense (unless you’re in the 9th circuit, but MAI has been swept under the rug).
I would say that legally, if you purchased Led Zep IV on vinyl, then recorded it to tape, you are not creating a legal copy. You purchased the information that comprises an album, not the mere media. If you transmute that information into another form, you still have a right to listen to that information. It doesn’t matter if you make recordings in 40 different formats, there is no additional transaction that is going on. Selling your recording to someone else will transfer your right to the information to them. The media is incedental.
Hence, downloading, while making another physical copy, isn’t a violation of what the law is about (provided you own a right to the information). Otherwise, you can bet Apple would be a smoking crater in the ground as they were sued to oblivion for allowing people to copy their CDs to the iPod. Similarly, when you pay for a song on iTunes, all you get is the information, which helps to illustrate that information is the product, not the media.
Imagine that you had a scratched copy of IV, and your friend had a good one. He makes a tape copy for you, but you have your own copy of the album on the shelf. I see no reason why you should be forced to make your own tape copy – you purchased the music, and the song remains the same no matter whose physical copy you listen to. The law, where tested, agrees.