I think there are a lot of parallels to ponzi schemes throughout the years.  A lot of ponzi schemes start at completely legitimate operations.  And then at some point along the path hardship causes people to dip into the reserves/holdings with the thought they can pay it all back.  But then circumstances arise or markets fall enough to push these past where they can hide and everything gets exposed.  I think some of the things in the BTC are just up front plain old scams.  However, it may be the case in the exchanges that some of them died in a similar manner.  Exchanges are under pressure to grow and handle greater trading demands.  If they don't have enough external funding it would be tempting to use account holder funds to help fund infrastructure expansions with the goal of just paying it back with transactions fees later.  However, it the market swings wildly this can get exposed.  Seeing that the end result is the same one has to just decide whether it was intentional or if it was just incompetence which turned criminal.