Marty87,
I am an apartment dweller, although not a luxury apartment dweller. I sit on a neighborhood scale planning committee for the neighborhood I live in, which is area with the highest residential density in Oregon. I am betting that this is a lower density than what is thought of as high density in Ireland. We have a great deal of high end apartments (for sale and for rent) in buildings ranging from 4 to 15 stories. Almost all of the new construction in the area, however, is townhouses. In the US, outside of very large urban cores, living in an apartment is seen as being less than ideal. The people who tend to buy luxury apartments are generally people who do not have children and people whose children who are now adults and have moved out. Apartments are not percieved as being suitable family housing in this country. While people do raise children in apartments, it is not the main stream idea of housing for families.
For that reason, apartments are seen as being part of the "life cycle of housing" for young people (who have not yet had children) and older people (whose children are now adults). It is not generally thought of as a sustainable long term community. You can certainly find examples, but they are not typical. I know about 80 people who live in my neighborhood- not a statistically accurate sample, but one to give you an example. Of these people, 1 has lived in an apartment for 12 years and 2 have lived together in an apartment for 6 years. None of them have children living at home. The rest of my neighbors live in houses, are saving up to purchase a house, or do not make enough money to ever be able to own a house or an apartment/condo.
You have to realize though, that America has much more land than many countries and is willing to spread housing out over much of it. Access to detached single family homes is vast here, unlike much of Europe.
I hope this helps!