Well they really are there. I don't know why you can't see them. Try the following to see the U-2.

Start FSX, select any aircraft, set the airport to LTBG, set the time of day to 10:45am, then click on FLY NOW. Once FSX is started at LTBG, right click in the middle of the screen and select Air Traffic you should see the U-2 in the list.