So those of us with dual nationality, who enter the US on our US passports and leave on our foreign passports, are going to get screwed. Lovely.
I'm more surprised they don't want to physically stamp your passport. Even though they already have a record of you entering and exiting the country, they've always liked to have physical passport stamps. And losing those makes a material difference in the case where another country cares where you've been.
>(b) Citizens
>Except as otherwise provided by the President and subject to such limitations and exceptions as the President may authorize and prescribe, it shall be unlawful for any citizen of the United States to depart from or enter, or attempt to depart from or enter, the United States unless he bears a valid United States passport.