Discovery Channel thinks we’ve had our fill of shows about the fancy fellows who make commercials at high-powered advertising agencies. The network is getting ready to launch a series about two infomercial stars who might not even be allowed into the hallways on AMC’s award-winning “Mad Men,” set on Madison Avenue during the 1960s, or TNT’s “Trust Me,” built around a present-day Chicago ad shop. “Pitchmen,” a 13-part original series premiering April 15 on Discovery, may be about infomercials—a form of advertising much of the media world looks down upon—but at least it has the virtue of being a real...