A full "sole purpose" statement is still absent from the 2010 NPR
The US 2010 Nuclear Posture Review presents deterrence as the fundamental role of nuclear weapons. It doesn't state that deterrence is their sole purpose. In other words, threatening to use the nuclear force is still viewed as a coercion instrument.
On the other hand, the NPR states that the United States will continue to strengthen conventional capabilities and reduce the role of nuclear weapons in deterring non-nuclear attacks, with the objective of making deterrence of nuclear attack on the United States or our allies and partners the sole purpose of U.S. nuclear weapons.