BTW, reading the actual PDF of the poll results, the very first page says this:

Interviews with 1,008 adult Americans conducted by telephone by ORC International on August 5-7, 2011. The margin of sampling error for results based on the total sample is plus or minus 3 percentage points. The sample also includes 930
interviews among registered voters (plus or minus 3 percentage
points).

The sample includes 808 interviews among landline respondents
and 200 interviews among cell phone respondents

If I’m reading that correctly, 930 out of the 1008 people they interviewed were registered to vote.