When the question in the title is posed, they aren't talking about the laugh track, the jokes, the plot, or even the sets. This is about the three-camera technique, which was developed by German filmmaker Karl Freund, and worked so well in TV shows that eventually all sitcoms used it. It's not just the cameras, but also the studio audience and the lighting that give it a particular style. Vox explains the three-camera technique, why it works, and how it became so ubiquitous. -via Laughing Squid
And while we are at it, I wonder which genius decided to cajole Freund into working on The Lucy Show, I am betting it was Desi.