It's easy to dismiss the importance of ABC's announcement Wednesday that Diane Sawyer is taking over the "World News" anchor chair from Charlie Gibson at the beginning of 2010.

After all, nobody watches those evening newscasts anymore.

That's the conventional wisdom, and it is true that the audience has been dropping for years for what once was the main source of TV news. But Nielsen Media Research numbers compiled by the TV Newser blog show that a combined audience of around 20 million people is still watching the half hour of news that airs at 5:30 p.m. in the Central time zone. When it's colder outside, that audience could get closer to 25 million, depending on the week.

In July, the combined prime-time audience for Fox News Channel, CNN and MSNBC was less than 4 million people, according to Nielsen numbers. And that's during the part of the day when the total TV audience is larger than it is at 5:30 p.m.

Demographics-wise, the evening newscasts have always attracted an older audience. But the addition of a second female anchor (CBS put Katie Couric in Walter Cronkite's old chair back three years ago this week) shows that there still is a target audience beyond retirees. Daytime TV, after all, has a heavily female audience that has Oprah and other syndicated talkers, a few game shows and a diminishing number of soaps. These women aren't traditional news viewers and attracting them was clearly behind the choice of Couric.

Couric's pick didn't translate into a ratings win for the third place network, but the network shows no signs of giving up on its attempts to build her audience.

The 66-year-old Gibson, who steps down at the end of the year, plays to the traditional news audience with memories of paternal anchors like Cronkite and John Chancellor. Williams, at 50, is the youngster on the block. Couric is 52 and Sawyer turns 64 in December.

Ultimately, the future lies beyond these half-hour evening newscasts, no matter who's in the anchor chair.

They once broke news, but a 24-hour cable news cycle and the Internet have turned them into nightly magazines heavy on features, health stories and consumer reports (the very type of "news" that is aimed at female viewers.)

But they won't be disappearing for a while, since it's hard to ignore 20 million nightly viewers.