Diosadentro,
What actually happens is some kind person actually buys the cd and decides that he wants to share it. So he basically rips the cd (remember now that he is the owner of the cd since he has purchased it with his own money) with the songs now on his computer stored as an mp3. He then uploads it onto his site or loads it on a tracker program which i won't mention. People download of this and basically it becomes known as a file sharing program. So it no longer goes against the copyright laws.
On the other hand these sites make money by saying that by downloading from us you are doing it the legal way. Think of it, they sell each track for 0.99c or even 0.49c for that matter. If an album has 15 tracks on it for e.g. that will cost the buyer $15. Im guessing if you walk down to the store you could probably get the cd a lesser price or the same. Makes no difference those sites make their money anyway.
Peace
It might be that way in the Land Down Under (which I highly doubt) but it isn't that way in the US.
Basically, you're saying that I can go to the store, buy a book and since I now own that copy of the book I can take it to a copy center, make 100 copies and give them to all my friends.
You might want to ask the copyright owner if he/she agrees with you.
FWIW, I am the owner of several copyrights, and it is never okay with me if you copy my stuff without permission.