Seriously why are people from different cantons getting involved with this? Each canton has different tax rates.

As Hash said, if you earn under 120k your quellensteuer is seen as your final tax bill and includes your federal, cantonal and community taxes. It is set at the average level for the canton, including usual deductions.

The only thing you haven't included in your calcs is BVG, which I believe is a minimum of 3.5% of anything over around 25k.

I live in canton Zurich, earn more than the the salary you are talking about, pay a hell of a lot more than 3.5% BVG, am single with no children and take home 76% of my salary.