Question: If only 11% of Americans watched all or part of Obama's SOTU address, how did NRDC end up with a sample of registered voters featuring 92% SOTU viewers?

NRDC: Press Release - NRDC Post-State of the Union Poll: 60 Percent of Americans Support Presidential Action to Fight Ravages of Climate Change

WASHINGTON (February 13, 2013) – Sixty-five percent of Americans think that climate change is a serious problem and a substantial majority support President’s Obama using his authority to reduce its main cause, dangerous carbon pollution, according to a national poll of 1,218 registered voters conducted immediately after last night’s State of the Union speech for the Natural Resources Defense Council (NRDC).

Obama's State of the Union lowest-rated since 2000 - POLITICO.com

33.5 million Americans watched President Obama's State of the Union address last night, the lowest turnout since President Bill Clinton's final State of the Union address in 2000, according to newly released Nielsen ratings.

How many eligible voters are registered to vote in the United States

About 150 million. There are 207,643,594 eligible voters in the U.S. The census bureau estimates as of July have the US total population at 303,824,640.  [Update: Indur Goklany submitted a comment saying that the U.S. population is 315.1 million people.  Using that figure and 33.5 million American SOTU watchers, still only 11% watched]

The detailed poll results are here [PDF].

Question 1 was "Did you watch all or part of the State of the Union address?".  92% said yes, 8% said no.