Joshua: Maybe it's the delivery that's lacking?

I can't speak for my other fellow Americans, but I will say that with the exception of Native Americans, America lacks a universal ethnic identity. Many of us cleave to our ancestor's identities as a way of standing out from the homogenization of ethnicities prevalent in our American Culture (the "white/black/other" boxes we have to check on official documents, etc).

This isn't uncommon among other Euro-American cultures, visit a large city and you are likely to see bumperstickers in Polish, German, Welsh, etc... and during International sporting events, you are likely to see Americans with some sort of ethnic tie to a particular country cheering for a country they are hundreds of years removed from. In large cities, you are likely to find just about anyone with a "ski" at the end of their name celebrating their Slavic heritage with food, clothing, and decor within their homes... even if they are several generations removed. My mother-in-law still swears in Italian and cooks FANTASTIC Italian food on occasion, although she is a Vietnam veteran and was born in this country to Immigrant parents.

In short, it is a blatant attempt to reconnect with an Ethnic culture. In urban areas, it is not surprising to see Mexican Americans wearing cowboy clothing (and in cases of weddings, Central American Indian garb),even in my urban area where cows won't be found for at least an hour's drive. It isn't uncommon to see American citizens who are Indians, Orthodox Jews, and Muslim Arabs/Asians wearing ethnic garb.

It is not so much "playing" (as that insinuates something not taken seriously), as it is reconnecting with a long-forgotten past to define an intimate, personal identity. And therein lies the perceived insult when we are accused of "playing" at building our personal identity.

For those of you native Scots not born into this culture, it may seem odd, and we may seem not genuine, but you do not have this background of missing your ethnic identity, it's been there for you, forever.
As one who lived in the USA for nearly thirty years, who is married to an American, whose children are both British and American, and who was immersed in the life of the area we were in - with no contact with expatriates, although frequent visits to the UK - I strongly resonate to these sentiments insofar as I recognize that this is what drives large sections of the populace there.

Our local Greek Orthodox church, for example, consisted of a congregation of a couple of hundred, all of whom were instantly recognizable as of Greek extraction. They ate Greek food, held an annual Greek festival, and so on ...

It is true that many in the USA may not properly grasp the nature of the countries of origin of their forebears from the recent or distant past. It seems to me that it is equally true that many in the old country, who may not themselves live in multi-cultural areas of Britain, find it equally difficult to comprehend these perspectives.