It is quite possible that one could download the media, check it out, and delete it in disgust. Or they might download it to check it out, not knowing what it's all about, and decide to keep it. In that case the copyright holder has lost out on nothing more than a _potential_ sale, because without downloading it, the person would arguably never have known they even wanted it.
Even with this loss, it is still a mixed bag for the copyright holder, because there is also the very real possibility that they might listen to this downloaded version for awhile, and either get tired of the poor quality or decide they like this artist, and they either run out to the store to get an album, or next time they go to the store they see an album by this artist sitting on the shelf and buy it because of the previous exposure. In that case the RIAA has _gained_ a sale that they would not have seen otherwise. I know this happens because I have done this myself.
The real problem is when I see an album in the store, check the price tag, decide I can't afford it or don't want to spend the money, and then go download it off P2P while laughing at how much money I saved. In that case, they have definitely lost out on a sale.
But in order to squash this case, their approach is to squash the aforementioned two cases as well, which are perfectly reasonable approaches IMO (both can be seen as try-before-you-buy measures). They would have many less opponents if they focused on the third case alone, instead of getting hungry for control and trying to destroy all of the cases I mentioned.