imported workers, page-5

“It is concerning that 2 per cent of the program reported incomes less than the threshold income set by regulation,” Ms Wilshire said.

The report details that over 70 per cent of 457 visa holders intend to become permanent residents in the future.

http://www.migrationcouncil.org.au/news/media-releases/457-visa-program-is-more-than-temporary/

You forgot about the other Visa's that bring foreign workers into Australia -
Temporary work visas

400 - Temporary Work (Short Stay Activity)
401 - Temporary Work (Long Stay Activity)
403 - Temporary Work (International Relations)
416 - Seasonal Worker Program
420 - Temporary Work (Entertainment)
417 - Working Holiday
461 - New Zealand Citizen Family Relationship (Temporary)
462 - Work and Holiday
457 - Temporary Work (Skilled)
476 - Skilled - Recognised Graduate
485 - Temporary Graduate
488 - Superyacht Crew

http://www.macrobusiness.com.au/2014/05/the-457-visa-rort-revealed/