Adasta, they say that any person entering a new culture goes through three distinct stages:
1) Idealization - this is where they have a superficial knowledge of that culture and primarily see the attributes of it without the faults.
2) Disillusionment - this is where they get a more in-depth look at the culture and see some of the more negative traits that may lie under the surface and require more intimate knowledge or exposure to the culture. They are greatly disappointed at that stage that it is not all that they had believed it to be.
3) Middle ground - this is where the person starts to see both the negatives and positives of the culture. They may see some of the deeper reasons for what they may have perceived as negative attitudes or behaviours, or uncover some positives under the surface that they had not been aware of before. They realize that any culture has both good and bad traits that temper each other rather than perceiving one extreme or the other.
Perhaps some of what you are seeing is people expressing the first stage. They have seen the pleasant aspects of their cultural roots, without the accompanying negatives. The lack of direct, undilluted exposure allows for more idealization than if they were immersed in that culture back in Europe. They also are going to be more likely to overgeneralize and not see distinctions between individuals or smaller groups of people who may be from the same culture. Most exposure, even if direct, is for shorter periods of time, which allows the person to continue idealization and to have exposure to the more superficial aspects of that culture, such as food, dance, music, and festivals.
If I base my impression of a particular cultural group on a couple of days at the different Folkfest pavillions, or Chicago's Irishfest, a person I like, a vacation to one of those countries, or glowing oral tradition that has passed through several generations, I am likely to feel differently than if I have repeated, in-depth interaction and proximity with a large sample size of that culture's population.
Particularly in the US and Canada, people often intermarry with other cultural groups, which dillutes and softens some of the more abrasive aspects of that culture. With each generation removed, people become more homogenous and less like the people from their ancestors' original countries. Not only that, but their ancestors may have been slightly different kinds of people than their countrymen to even be willing to come in the first place (and therefore not accurately representative of the whole culture). The hardships they experienced tend to give people a sense of pride in their roots and interest in knowing more, without any in-depth rubber meets the road experience sometimes of the culture they are speaking about.
It sounds very romantic to say that your great-great-great grandmother was a Cherokee princess. It's quite a different thing to go and live on a reserve, or to even delve into what life in those times was actually like, or how women were treated (either by Europeans or by Aboriginal peoples), or what options were available to them at the time.
As much as there is to be proud of for the hardships people successfully came through, I think many of us may find our own ancestors difficult people to meet up with if we were to go back in time or see them through the light of our present day beliefs and outlooks. I see what you are saying on the one hand, Adasta - it is no particular accomplish to have had certain ancestors and many people in North America no longer actively are a part of a particular cultural tradition. At the same time, I think you may be oversimplifying it. Our roots do impact North Americans and our sense of identity more significantly because we have a very different history (where else in the world do you see that diverse of a mix of cultures making up the main fabric of their society?), and many of the events that impacted our ancestors are still within living memory.