The rain has severely messed up the original court assignments and broadcasting schedule. Venus was originally going to be second on court 1 on Sunday which would have been a fine court assignment. She was then rescheduled to 2nd on court 2 which I thought was wrong and could have been better decided, but the original intent was fine. Today she was on CC and she and Serena were originally scheduled to be 3rd on court 2, once again a fine assignment for doubles. Then you had a 2+ hour rain delay and a men's match that took 4 hours and backed up matches on that court and so the organizers most likely asked Venus and Serena did they want to be moved to a court that would be available quicker and they accepted. If Hewitt had lost the second set of his match the Sisters might still be out their now playing if the original court assignments and schedule had been kept.
The event can't afford to get any further behind so it was best that they got their match in no matter what court it was on. You have to remember they are trying to cram a GS size event into 9 days.

Singles matches ALWAYS take precedent over doubles and the singles matches that had yet to be played got priority. Believe me NBC and the tour would have much preferred to have the Williams vs the Germans on in the last hour over Azarenka and MJMS or Huber/Raymond vs the Radwanskas, but the weather and getting matches in didn't allow it. NBC will air the WS in doubles as long as there isn't a top man or woman in action which is something almost no other doubles team receives. The Bryan brothers doubles match was also moved to a non televised court and Federers doubles match was cancelled.
The comparisons you made with Basketball and Tiger Woods don't exactly work because Basketball isn't affected by weather as easily as tennis plus matchups are scheduled months in advance, making televising big games just a function of coordination. In golf there are usually 30 to 40 players out on the court at the same time and there are camera's set up at ever hole. If this had been Wimbledon (the GS) court 12 would have been televised, but since the networks whose studios (ESPN) are situated right behind court 12 aren't there the cameras weren't there either. Venus and Serena's doubles match not being televised was a byproduct of the weather, the heavy load of singles matches being played, the small number of courts that are televised for Olympic coverage and the limited option of courts to put them on. There really was no better place to put them in order for them to get their match completed. This rain has really hamstrung the event and they are doing the best they can to get matches in. Organizers sometimes just have to just throw players out on any old court so that the event can finish on time. It is true that a very select few are immune from this in Singles like Federer and Nadal, but Djokovic and even Murray have had to play on 2nd and 3rd courts when the weather forced it. I agree with you though that tennis often fails to capitalize and make the most of it's stars, but today's doubles match was not one of those instances. :shrug: