Apple is reportedly looking into the feasibility of letting users download a song from iTunes as many times as they want after they pay for it, a move that quite honestly should have been around for quite some time now. Right now, when you buy a song on iTunes, you get to download it once. From then on, it's up to you to keep track of that audio file and make sure you don't lose it. If you want to re-download it, you're SOL.
This becomes a hassle for users who have multiple media devices. If you buy a digital CD on one computer but then want to listen to it when you're on your laptop, you have to transfer over all the files. It's needlessly cumbersome, and now Apple seems to feel the same way.
The issue apparently isn't with Apple but with the record labels. Those companies are very strict with how they license out the digital rights to their music, and have agreed to a very specific set of guidelines. One of them is that users can only download the track once.
But that hasn't always been the industry standard. Back when Sonny offered Connect, its own digital music store, users could download a song up to five times after they paid for it, a feature that was largely advertised as a way to buy once and download on all your devices.
You would think iTunes would have significant pull, since it has a 70% market share in the digital music space. Nevertheless, it always blames the record labels. The same thing happened when people started calling for iTunes to offer MP3 downloads instead of Apple's DRM-laden proprietary format. Steve Jobs said it was the record labels' fault and issued an open letter urging them to be more open with their content.
It would seem that Apple stands to gain something by not offering unlimited downloads. I personally have re-purchased several iTunes songs, since Connect shut down, simply because I don't organize all of my digital content. It sure would be nice to know I could download songs again after I've already paid for them.