From NBC's Olympics coverage website:
"For the first time by a U.S. broadcaster at a Summer Olympics, NBC will provide high definition coverage. NBC's separate, unique HDTV coverage on NBC's digital affiliates, presented by Sony Electronics Inc., will provide HDTV coverage on delay of six sports from the only main Olympic venues provided in high definition by the Olympic host broadcaster. Those sports include swimming, diving, gymnastics, track and field, medal rounds of basketball and the men's soccer gold medal final. The HDTV coverage will total 399 hours and is a completely different production from the standard definition broadcast on the network. NBC has 124 HDTV affiliates with the potential to cover 86 percent of the country."
This sounds like they plan to separate the NBC SD & HD broadcasting during the Olympics, rather than having the HD channel (i.e., 105) mirror the output on the SD channel (5).