Less than a week into the Paris Olympics, NBC Universal executives are climbing atop the medal stand. The event has been a significant success for the company broadcasting and streaming it in the United States. NBC has already set a record for advertising revenue, viewership is up significantly and its biggest fear — that people would tune out NBC’s prime-time telecast because they could watch events live during the day — hasn’t materialized. “Clearly, the Olympics are back,” said Mark Lazarus, chairman of the NBC Universal Media Group, on Thursday.