Alice you're correct that sometimes the notion that "you get the exposure" in lieu of pay is not a good deal for the artist. As one who must choose his "give away" opportunities carefully, I do just that; I choose carefully which of those opportunities really are worthwhile.

For me the Youtube clips are well worthwhile. I do not earn at the level that I can afford a true advertising budget, but Youtube and few others make up for that. The clips there are not replacing the "product" I sell - they are giving samples, and providing access to links where I sell the product. It works. I've had 10s of thousands of play at Youtube and regular notes in on-line purchases saying that the buyer found the album through Youtube (or similar engines).