When I was an intern at the UPN affiliate in Chicago in 1996, among my duties was writing episodic voiceover promos...e.g., "Mitch is in hot water on 'Baywatch,' next on UPN Power 50." They were vetted by the promotions director before they actually got recorded and went on the air, but still, the fact that this is something they had interns do should tell you how highly esteemed the art of writing voiceover promos is in television land.
Actually, when I watched SoapNet for the first time last week, to see if my closed captions were properly showing up on their "Days of Our Lives" same-day repeats, I was a little surprised to discover that they did only a voiceover promo during the closing credits.