Nielsen Begins Tracking College Students

It's unclear to me if college students -- notoriously difficult to track since they usually watched in grouops -- are reflected in the overnight ratings for "Heroes" and "24." I doubt it, since the shows should have jumped up more in viewership if they were. But this article says Nielsen will begin with a sample of 130 college students. Okay, I understand how sampling and polling works. But with cable boxes in everyone's home, why can't Nielsen use a MUCH bigger measurement of who is watching what? Just as SoundScan measures exactly how many CDs are sold at the major retailers (covering some 90% of the market), I would have thought by now that we'd be tracking literally what everyone is watching, rather than still using tiny samples, diaries and the like.