I'd be interested in this as well. My impression is that it isn't as severe as many believe and the phenomena is equally prevalent in tech as well (i.e. people doing startups who would otherwise do something more productive).

From what I've observed the people going into finance are a separate class of people from those who want to be doing research.

A further issue is that the quality of life for PhDs is low. Something like 1% of PhDs end up with tenure track positions and many are stuck doing years of postdoc work. It's easy to blame finance, but there are problems with other parts of our society that are driving peoples actions as well.