AAPL paid 30.5% taxes on all sales in North America and South America. AAPL paid 0% taxes to US government on all sales in Europe, Asia and other parts of the world because AAPL set up their international office in Ireland where there is almost zero corporation tax. AAPL argued that they already paid Ireland tax so they should pay no tax to US government when they transfer the money from Ireland to USA.
Why does Ireland only charge AAPL 1.5% tax? Because it is free money. They do nothing but collect the money while AAPL has most intelectual properties developed in US and Ireland office has only two employees. Closely examine the scheme, everyone could see Apple is worse than Enron.
So Ireland has maximal 2% corporation tax and all big US companies have subsidiaries there to take advantage of it. But Ireland is still broke. Most likely because it gets lots of free money so the government spends it unwisely.
The winners are big companies ant their CEOs. The losers are Ireland, USA, US tax payers and small US companies that can't setup Ireland tax shelters.