From my experience reading US patents/applications, they aren't just vague like that. They start out specific and then add additional claims which expand it. So they will have some claim about a cart with a specific number of wheels, but in later claims they'll add language to generalize so any number of wheels are covered. There are also figures and detailed descriptions which are separate from the claims which aim to make clearer. Pretty much any one I have read seems to make it clear enough create the device.