Power of Marketing
One thing I used to find amusing, is that when I was in school some people knew more about the aebersold play a longs rather then actual jazz recordings. When Brandord Marsalis used to have his forum, he would recommend that you just play with the records you have. I think what sells a lot of the play a longs is that it's an ego booster, you get to be "the cat", sitting in with Dexter Gordon and Woody Shaw's Homecoming rhythm section on the Woody Shaw play a long is fun, have to admit (sorry about that awful sentence). That's what Jamey says, "builds confidence". Confidence in the living room I say. When you first start jamming for real, you realize what it really feels like to play, there is no substitute.