In NZ we have virtually no deductions ... No carve outs for special interests. So no schedule A .... But more importantly that means that employer withholding is simple. As an employer it's also trivial to do PAYE and get it right.

Also we have no capital gains tax (a mistake IMHO). Tax on interest, (and a second income) is withheld by banks at our nominal marginal rate.

In practice if the govt doesn't care about the tax on your cabbage patch doll, unless you are selling thousands of them it costs more to collect that tax than they would receive