Michael Dowling, GM of Nielsen says, "In game measurement of product, placement is the next frontier." To accomplish the measurement, one would need a separate in-home device similar to those now used to track TV viewing habits. Activision is the only game company working directly with Nielsen at this point however I would imagine that some of the other big names (EA, Ubisoft) will be on board once the technology is up and running.
The goal of all of this measuring is to establish a baseline for the cost of ads in games. Think about how NBC, ABC, et al, establish their ad rates for the year. The hope is that a similar formula could be applied to games.
The inherent problem, of course, is that prior to launch, a game publisher doesn't really know if a game is going to be successful or not, unlike a long-running TV series with an established past. This doesn't bode well for new or untested games. However, there are sure hits out there like the upcoming, "Halo 2," and "Half-Life 2."
It all comes down to this: with the cost of video game production skyrocketing, a hefty check from Nokia or Adidas or Slim Jim sure does help. Video game companies want a way to solidify and codify that revenue.