2) Yes (though in some cases downloading them isn't illegal so long as you don't use them).
3) Yes (illegal everywhere not just USA).
4) Depends on the specific application. Programs such as alcohol, blindwrite, etc that preserve the copy protection are legal. Programs such as Dvd Decrypter that have the primary purpose of stripping the protection are not (just ask 321 Studios).
So would a website that offered cracks for download be breaking the law regardless of where it was hosted and run from as long as US citizens were able to access it?
The relevant laws are those of the place where the website is located not those of the USA. However, since offering cracks, keygens etc isn't legal anywhere, it doesn't make much much difference (though, of course, the authorities of many countries are far more lax than those of the USA in enforcing copyright laws).