*I think the opening post is yet another example of the
greed 
that is so rampant/overwhelmingly obvious in broadcast media; television more than radio, I think. They want our
attention** so that (they hope) we will also watch their
commercials and then (they hope even more)
buy the advertised products. If we do, they can then go to the companies that paid them for the ads and say, "Gee, look how much money you made thanks to advertising through us; now why don't you either pay us a higher rate for the same ads, or pay us more to run more ads?" GRRRRRR!!!!!!!!
**And one way to try to hold attention is to give "teasers" about what's coming next. Even newscasts do it, as in, "Are we in for a terrible storm? Tune in to our weather forecast after the break and find out".
again.
In the Joan Rivers-type ex., I think it's probably more due to having to speak "off the cuff" than anything. Apparently dead air time is the ultimate no-no, so they blather without necessarily thinking first.
