I really don't think 9/11 has anything to do with it. In the days that followed 9/11 temporary boundaries were set in place to prevent boats from being too close to dams - I know because I was pulled over for it at Ky Dam (no buoys were placed, and the boundary lines were based on trees on the bank - I certainly missed the memo about the "tree boundary line"). After a few weeks everything was back to normal.

The buoys are there for safety purposes. I too have heard loudspeakers at Barren tell boats to get out of the no boat zone. If there were an emergency drawdown or something along that lines, being in that area would not be a good thing!