When "talk" encompasses everything from the Regis and Ellen style shows to Jerry and Maury, it's a broad brush to paint with. Like all broadcast, the audience is smaller than a quarter century ago or more thanks to audience fragmentation; that said, as a broad genre, talk still does well. Yes, long-running shows inevitably decline, and there are busts on the launchpad as in every genre, but there's still a good audience--and thus $ to be made--when a format or particular show breaks through (witness The View in the first place).
As for the economics of a half-hour soap, it could be cheaper than an hour, as generally you're going to require less labor costs overall in a thrity minute show. I took a look at the opening credits, and lots of the cast members listed look to be youngsters, which certainly makes things a bit cheaper. But more importantly than any of that is that CBS makes a big chunk of change from international distribution, where the show does huge numbers.
