It's not just music games like Guitar Hero, Rock Band, Singstar and the like that are helping.
EA has collected statistics showing that sales of music included in their games - i.e. music used as EA Trax - increases after those games are released. I'd imagine the record labels for the bands featured in the radio stations in Grand Theft Auto would agree (even though nobody in Britain will sell me "Inside the Cage (David Gilmour Girls remix)" by Juliette and the Licks).
Personally, I find it a very good way to discover new music.