I disagree, but thats just me.
I think some DVDs are worth the price and some are not. With Piano Lessons, you learn one, maybe two songs for $50. With a DVD, you can learn many many many songs, among other things like preacher chords and different grooves for the same price. With DVDS, you can pause and rewind, and go back to it whenever you want.
If you think about it in business terms, piano lessons are an expense, and DVDs are an asset. Once your hour is up, that $50 is gone, and you better hope you remember everything you learned. With DVDs, even though you paid $50, you still have something that you can go back to when you need to.
DVDs arent for everybody, and neither are lessons.