But the affiliates are complaining because ABC and NBC provide rich content in the last few minutes before the 11 pm news.
A CBS spokesperson says the network's 10 p.m. performance has led to a 15% ratings increase in late local news, compared to last fall, for affiliates in Local People Meter markets.
From what I can tell, CBS is providing a pretty good lead in:
The affiliates produced a study from Frank N. Magid Associates at the May meeting that broke down exactly what the networks air in the 10-11 hour. General managers who saw it said ABC and NBC were content-rich in the last 10 minutes; CBS, one says, was “a train wreck” of spots, credits and teasers. CBS countered with its own research about the network's effectiveness in driving viewers to late news, and the two parties left at an impasse. (CBS, of course, has ample skin in the local news game, with 14 O&Os.)
Of course it isn't necessarily the result of actions by CBS. From another article on the same B&C page:
While NBC affiliates are hoping that The Jay Leno Show can find its comfortable ratings middle ground, a number of CBS affiliates say the demise of scripted dramas at 10 p.m. on NBC has been a boon for their prime—and their late news. The general managers at various CBS affiliates say they're seeing ratings gains on what used to be their weaker nights, with a ratings generator such as NBC's Law & Order out of the 10 p.m. picture.
...NBC affiliates keep emphasizing that Leno must be measured over the course of a year; it will be fresh for 46 weeks, a considerable advantage when the competition is in reruns....