However, for 2011 the FICA rate for employees is 4.2% instead of 6.2%, so the self-employment tax remains effectively 7.65%. But that's only for the first $106,800 in earnings - everything above that is not subject to FICA and Medicare for employer and employee.
It is a myth that America is a low tax nation.
http://en.wikipedia.org/wiki/Government_spending#Government_...
In American those taxes provide a strong military. Most of the rest of the world are very poorly equipped by comparison. Other countries get health care and education.
The differences in tax between the US and Australia are not so much in the headline rates as in the deductions.
In the US mortgage interest on a home you live in is tax deductible.
And in the US you get taxed as an economic unit with your spouse and children.
So a home owner with a big mortgage and a spouse at home looking after kids pays much less tax in the US.
Also the overhead of running a corporation (including lawyer, accountant, payroll, and general insurance) is not much if you're making over $100/hr. It is certainly less than 26.7% (ie, $75 of every $175 minus 15.3%) worth. Most of these costs are fixed, not variable.
I've found a good (albeit a bit conservative) rule-of-thumb is to convert the hourly wage into the yearly salary. Working as a consultant for $175/hour is similar to being employed at $175K/year.
EDIT: The U.S. federal self-employment tax for 2011 is 13.3% (15.3% was for 2010).