My .03 cents.....
I think that it is the events and affects associated with washing that MAY promote growth. I mean the removal of sebum and dirt that may be clogging pores and inhibiting growth. Also, if one massages the scalp while "washing", it benefits the follicles, which would help with growth.
This would mean that it doesn't matter HOW one "washes", as long as the affect is the same. I only wash with shampoo when it's time to retouch, so my hair will only see shampoo approx. 4 times per year. However, my hair and scalp are still clean and my hair IS growing. I just need to stop cutting it! /images/graemlins/smile.gif