They do that all the time. Personally, I prefer to the entire album collection over a single song but those free songs can help you decide if you'd like to get the rest of the album. I also love their 50 albums for $5 each promo although I'm not interested in any of the selections for September which is odd. I can usually find an album or two in the 50 that I don't have and want.
Yeah Amazon does it quite a bit but this is the biggest selection I've seen. And as far as buying the album or just one track, I almost always buy single songs as opposed to the whole track. I often dislike most of what is on the CD save for a couple of songs.