The American upper middle and upper classes of WASP ancestry seem to be extremely well-connected to the British Royal families, as anybody who studied the British middle tthrough upper classes would expect. I wonder if they and their counterparts in the five Dominions (Canada, Newfoundland, Australia, New Zealand and South Africa) might not even be better connected than the British, seeing as many of the earliest emigrants to the colonies seem to have been top heavy in younger sons of the gentry and upper classes seeking farmland and a living that increasingly became impossible for aristocrats and gentry in the UK as the colonies outproduced the Mother Countries in agrarian products such as wheat, cattle, and fruit.
On the other hand, I wonder if this could be merely a matter of perspective: it is always easier to trace the ancestry of the well-to-do with the leisure and the taste for genealogy. As you go back in time you lose the poor (except for criminal records and charity records) and then the middle classes and gradually even the aristocracy and royalty are replaced by saints, culture heroes, and barbarian chieftains of various tribes. There's a lot of factors that bias our data from the Genghis Khan effect through the Founder effect and various kinds of data-collecting bias.