Bill gates on tax.

[kılıç_mehmet]

One should pay tax according to one's income, that much is true.

Indeed.

Plus, aren't Muslims OBLIGED by Quranic admonition to give a fixed percentage of their income to the poor? (2.5% I think)

Well, religious "taxes" are not collected by the government.
People here pay their usual taxes, and we're taxed so much on everything, I'd say if we were to pay zakat, we'd have to cut off ounces of our own flesh to give to the poor.
Only the rather more wealthy and more devout individuals do so.
Those in rural areas give it out from their own agricultural yields, rather than in hard currency.