Earlier quoted context omitted.
That's because they are deferring the taxes on the ex-US money. It's a 401k in the US. It's a tax deferment, not a tax break. If your effective rate went from 35% to 25% due to your 401k contribution, you still end up paying 35%, just not right now.
No, you don't end up paying 35%. Part of the advantages of a 401k come from distributing dollars being taxed at a high marginal rate to another year when they are taxed at a lower marginal rate.
But if you put a lot in, the fact you HAVE to start taking money out at a certain again AND it all gets taxed before you die means you pretty much end up paying the taxes anyways (or more if rates have gone up).