The big difference is that the US will sting you for tax wherever you are in the world, whereas most will only tax residents (complexities in terms of tax treat

The big difference is that the US will sting you for tax wherever you are in the world, whereas most will only tax residents (complexities in terms of tax treaties notwithstanding). Hence in both cases they are both looking to realise gains at the point where they no longer have control over the taxes being charged. A `penalty` for leaving their tax jurisdiction, notionally for the tax they are 'owed'.