ESRB Rates Games Without Playing Them?

In what seems like an odd disconnect, the ESRB apparently rates some video games without actually playing them. In an interview with PC Magazine, the president of the ESRB describes the ratings process, and notes that it involves reviewing a written form and watching a DVD depicting "pertinent content" from the game. However, she doesn't say anything about raters actually playing the game. The ESRB website says only that the process "may involve" the raters playing the game.

If it's actually the case that the raters don't play the game, then this seems strange to me - sort of like rating a movie based on clips and a written description. How can raters get an idea of the overall feel and context of game content without actually playing, at least for an hour or two?