Immigrants can be divided into two categories #. Highly skilled (enng/doctors/scientist etc) #. Students who come here on the lure of getting citizenship
Majority of highly skilled immigrants are not rich when they come(your 50% figure is an exageration), Category one immigrants are higly qualified and get into high paying job. I am not so sure about category two.
In my network(Mostly ENGGS) there are lots of highly qualified immigrants who have already gone back and many are seriously considering going back, due to very high living cost(ie even at high income here they are worse off than in UK/US/singapore/india etc) Indian IT enggs who went back are those who have gained Au citizenship(insurance?)
PS: IT enggs/architects with more than 7/8 yrs exp are very well paid around the globe.
One immigrant PHD scientist I was talking to the other day said Its better off to be an plumber or tiler in canberra than to be an PHD (he works for CSIRO and considering going back to singapore)
Have a look at http://www.expatforum.com/articles/cost-of-living/cost-of-living-in-australia.html#idc-cover
