According to copyright law most places (but clearly not in France anymore), legal copying will not result in loss in the artist income (theoretically). An artist can never expect to sell more than one example of a piece of art to each customer for his own use. So if you buy a record, it would be no problem for the artist if you made ten or twenty copies for your own use, since private copying would never result in a loss that needs to be compensated. On the other hand: If you give away a home made copy as a present to a friend, the artist looses a potential buyer. That's his potential loss. Since blank tapes, CD-R's etc make it possible to distribute the music outside the houshold, it could result in a loss for the artist. Hence the tax.
In short: legal copying should not result in loss, therefore no comensation needed. Blanks increas the risk of illegal copying, therefor a need for comensation. Hence the need for tax on the blanks.
Anyway, I'm learning a lot here. Thanks, ds1984!
I guess it's still like this most places, but strangely enough IMO, not in France.