I thought this little snippet fromt the npd release would be a good addition. It shows sample size, etc.

Methodology
Data was collected via an online survey of 20,240 NPD Consumer Panel members ages 2 and older. Respondents age 2-12 were captured via surrogate reporting whereby the female parent (age 21-55) brings her child to computer to answer questions, either with or without parent’s assistance. In order to qualify as an online gamer, respondents had to use one or more of the following systems to play games online: Nintendo DS/DS Lite handheld system, Nintendo Wii, PlayStation 2, PlayStation 3, Sony PSP handheld system, Xbox, Xbox 360 or PC. Gamers overall (whether online or offline) were included in the study as well. Fieldwork was conducted from January 11 –February 5, 2008.

 And another look at the data.

http://www.gamasutra.com/php-bin/news_index.php?story=18107 

NPD says the number of game-players has grown from its last study, up from 64 percent the year prior. More than half of that 72 percent, says NPD play games online, but relative to "total U.S. population," online gamers have only risen slightly from 40 percent in 2007 to 42 percent.

90 percent of online gamers said the PC was their platform of choice, compared to 19 percent for console and portable systems, and 3 percent for cell phones. Younger players make up a good percentage of online players, with 40 percent of online gamers between 2 and 17, with 18-24 year olds only making up 10 percent.

As for online console players, 50 percent were Xbox 360 gamers, who spent the most time per week playing online compared to PC and PS3 owners. Finally, NPD says only three percent of respondents said they owned two of the three next-gen consoles, and only 2 percent said they owned all three.