> some upper-middle class teenagers, little more
  > than pocket change

I think that my parents would be considered upper-middle class and I've never thought that $200 was pocket-change.

  > Three days in jail (or juvenile detention), on
  > the other hand is most likely a novel and frightening
  > experience that's actually likely to discourage similar
  > behavior in the future.

For some. For others it might just allow them to find bad role models more effectively.