America and the ethnic question

I've had some interesting ethnic identity experiences every once in a while in Germany. For instance, today at a doctor's office I was asked about the ethnic origins of my family name "Donahue." I said it was Irish. The nurse then thought that I was of Irish nationality and was quite surprised when later on I told her that I was American but that my family name was of Irish heritage. This was not the first time this has happened.

I'm getting the feeling that most Americans identify themselves in Germany simply as American. They don't fully explain their ethnic heritages as they would in the States. All talk of Irish, Italian, Mexican, etc. - American falls by the wayside and they are just "American." Homogeneity smothers the specificity of ethnic identity, something that would never happen on the other side of the Atlantic.