Yes, you're right in that most websites seem to suggest the Freedom of Information Requests for foreign citizens.
However, US citizens can indeed do this.
Chris Guillebeau documents his process of doing this and he's a US citizen (who has visited every country in the world).
He got back from his request:
- A letter with an official response from the U.S. Customs and Border Protection
- A long list (14 pages) of my international arrivals and departures
- Another long list (8 pages) of various flight data, discussed below