Perhaps a mistake concerning the Frank Lloyd Wright nomination, or an additional serial site.
The link names 11 sites that make up the nomination, however only 10 sites have been listed in the nomination. So it's either a mistake or this site has been added to the nomination.
Herbert and Katherine Jacobs House, Madison, Wisconsin(constructed in 1937 and is considered by most to be the first Usonian home.)
*I guess I should be happy, as someone who grew up in Wisconsin, there may now be 3 FLW sites included in this WH nomination.
There are alot of sites that keep coming up for the next US nomination to be reviewed by the WHC.
San Antonio Missions
Frank Lloyd Wright Buildings
Hopewell Ceremonial Earthworks & Serpent Mound
Petrified Forest National Park
It is still not guranteed that there will be a site ready for the 2013 WHC, but it is clear 2014 will be a big year for the US world heritage program.
Links concerning the Frank Lloyd Wright Buildings nomination for 2014http://www.scpr.org/news/2011/07/13/cabinet-secretary-nominates-hollyhock-house-un-wo r/http://laist.com/2011/07/13/frank_lloyd_wrights_hollyhock_house_1.php