Of course they are still able to vote as an expat in US national elections via absentee ballet; i.e. the same way you vote when you’re an expat living overseas just for work.
And as far as I know, regardless how long you live overseas you can continue to vote absentee as long as you keep-up your registration in the last place you lived.
So in other words, these people with dual-citizenship can vote in elections for both countries. Think about it....that pretty scary.
It's my understanding that you have to maintain a US residence in order to vote. That is, you vote in a state, not in the United States. E.g., a natural born Puerto Rican over the age of 35 is eligible to run for president, but can't vote for himself unless he moves to the mainland first.
“So in other words, these people with dual-citizenship can vote in elections for both countries. Think about it....that pretty scary.”
No. You are the one who is scary because of your lack of understanding and knowledge.