That seemed to be the case earlier in the year but you can't really say that when 67 million people watched the first debate. Only 52 million watched the first debate in 2008.
The first debate in 2008 was on a Friday night, which is one of the least-watched nights on television. The Veep and later 2008 Presidential debates got higher ratings.
Palin-Biden was watched by 70 million. The second McCain-Obama debate was watched by 63.2 - 66 million, depending on the estimate.Turnout will be down from '08. This election isn't nearly as historical. Everything points to lower turnout from the 18-29 set and perhaps African-Americans.