Bratwurst and wieners are indeed different sausages in the US, but funnily enough you would never boil a wiener here, they are always grilled or microwaved in a pinch. Whereas brats are somewhat commonly boiled (often in beer) to cook the inside, then finished on the grill to brown the outside. Though I personally cook them entirely on the grill, as I think the boiling method is somewhat cheating.