Lack of grey income from dodgy private tutoring jobs on the side, lack of participation in corrupt activities such as accepting bribes/hongbaos, lack of social insurance payments towards a house that the Chinese staff get. Not to mention the lack of that generous spring festival bonus. Several things really.

Also many younger teachers are paying off student loans in the U.S.

I also have reason to believe that the '5 times more' comment is a bullshit exaggerated figure at TCs, but at universities it is actually the case that Chinese professors get paid far more than foreign teachers, even though their work is definitely inferior to that of the FT. Those shiny new cars don't pay for themselves, you know!