In a presentation at an industry conference this afternoon, Comcast (NSDQ: CMCSA) chairman and CEO Brian Roberts offered his rationale for the cable operator’s decision to purchase 51 percent of NBC Universal (NYSE: GE) in a deal valued at $30 billion: it’s about getting better production values and scale for its own programming channels. Speaking at the Citi Global Entertainment, Media & Telecommunications Conference in San Francisco, Roberts said that NBC’s worst channel, Oxygen, makes more than Comcast’s best channel, E! Entertainment. That doesn’t mean he thinks Comcast’s channels aren’t doing well—after a decade in the programming business, “Every single asset we have has made money for our shareholders and has grown,” he said. It’s just that NBCU’s channels are so much stronger. By mixing and matching program assets between Comcast’s channels and NBCU’s, coupled with Comcast’s distribution strength, both companies should benefit, he said.