[glenneroo]

If the government really cared, wouldn't/couldn't they just force banks to forbid transactions with known tax havens?

[runako]

This isn't about tax havens, it's about the fact that US law levies taxes on corporate income earned anywhere in the world.

So iPhones sold in Sweden or France (not tax havens) generate tax liability in the US. This tax is only due when the profits of those sales are brought back to the US. Companies like Apple therefore have an incentive to keep overseas profits generated outside the US.