Here is the breakdown for the quants at the bank I worked for in 1995-1999 (I may have forgotten a few people):
Cornell physics PhDs: 3
Harvard physics PhDs: 2
Princeton physics PhDs: 2
Univ of Penn physics PhD: 1
Other physics PhDs: 2
Cornell applied math PhD: 1
Other applied math PhD: 1
Cornell mechanical engineering PhD: 1
Univ of Chicago finance PhD: 1
So, if by "dropout" you mean that they didn't complete their PhDs, then no, that's wrong. If by "dropout" you mean people leaving physics, then yes, it's very common (especially for theorists -- all physicists on the list above where theorists except maybe one or two).
Cornell physics PhDs: 3
Harvard physics PhDs: 2
Princeton physics PhDs: 2
Univ of Penn physics PhD: 1
Other physics PhDs: 2
Cornell applied math PhD: 1
Other applied math PhD: 1
Cornell mechanical engineering PhD: 1
Univ of Chicago finance PhD: 1
So, if by "dropout" you mean that they didn't complete their PhDs, then no, that's wrong. If by "dropout" you mean people leaving physics, then yes, it's very common (especially for theorists -- all physicists on the list above where theorists except maybe one or two).