In one of the articles I read while following links from here ( http://www.tarpityoga.com/how.html ) they say:

  You also have to completely believe in the TMS diagnosis.
  That means that you have to completely accept the fact
  that your symptoms are emotionally induced. If you still
  believe that there may be something physically or 
  structurally "wrong" with you, you're not yet "cured."
  You're not paying attention to the underlying emotions,
  which means that the symptoms can still work as a 
  distraction, and it's likely that they will return. 

Sounds like a self-imposed placebo to me. If it works it's still good, of course; it'd be very useful for "standard" medicine to learn how to use the placebo efficiently and ethically.

It also sounds like a good excuse to explain the people who aren't helped by the therapy - if they don't get better they don't believe in it enough and have themselves to blame (or they have the wrong diagnosis).