I do not know where the suprise on all this comes from. The dirty sock smell has been apparent on aircraft for over 30 years or more. The most common affected aircraft were the B757 and the BAe146 series of aircraft It was common on the ALF502 engine where one of the seals used to fail, a lot of history on this in the Australian press going back to the 1980's.
Manufacturers always deny there is a problem, blame maintenance practises, but fault lies in the design of the engine air system. Hopefully, with the 787 which is bleedless, this will go away, but not on older aircraft.