Why some naturalized US citizens swear a different Oath of Allegiance

CSMonitor: Why some naturalized US citizens swear a different Oath of Allegiance
by Sarah Caspari, JULY 22, 2015
The White House clarified which naturalization candidates are exempt from vowing to serve in the US military if called. (read the whole article)

Also see: USCIS: USCIS Clarifies Eligibility Requirements for Modifications to the Oath of Allegiance