This change was born of the Runway Safety Program, which is apparently behind the "line up and wait" ICAO phraseology adoption as well.

Here's the National Runway Safety Plan 2009-2011 which is an interesting read.  

Bottom line from this paragraph:

4.4 Performance Targets
Under the goal of “Increased Safety, Objective 3, Reduce the risk of runway incursions,”
the FAA Flight Plan 2009 – 2013 contains the following performance target:
     â€œBy the end of FY 2013, reduce total runway incursions by 10 percent from the FY 2008 baseline.”

This is a specific measurable goal which will supersede others, so expect even more FAA procedural and technological changes.