This is another strange problem. I noticed that recent shots with any of 3 Nikon cameras, D3, D4 and D300s lack the distance data in CS6 Bridge. But older shots do. I narrowed the change to about June 10, 2012. Before this they have the subject distance and June 12 pictures and later don't. It seems that this is the time when I configured or installed CS6 which was a free upgrade after getting CS5.1
When I open CS5.1 Bridge though, even the most recent shots have subject distance.