Indeed. But this cheaper, faster method might also lead to too many people hearing about the band and liking the music. We wouldn't want that. We would rather sell 100 cassettes for $2 each and have 20 true fans.
Seriously though, I would not be surprised to see MP3s from these bands as an additional marketing tool.
The cassettes are likely to be viewed by the audience as collectibles, creating word-of-mouth marketing. They are "social objects" to use Hugh Macleod's insightful phrase.
My son was wearing a t-shirt made by a tiny shop in San Diego. You only own this shirt if you know the maker. He was touring a college to see if he wanted to apply. He was accosted by a student. "Where did you get that shirt?" They were both friends of the maker.
This creates a sense of "I belong".
Interesting side note. This shirt -- and the tiny company -- wildly and deliberately violates trademark law. Not to make money, but for the same reason (I think) that musicians use samples.