Reuters is reporting all the takeoffs and landings from England. If we wanted to keep those thing secret, we would probably arrest Reuters reporters. I think the Air Force is very confident of its air supremacy and does not care if the Iraqi generals with internet acces know when to expect our B-52's. I think it is an aspect of PSYOP.
It' a small place, and it's full of B-1Bs, B-2s and tankers. I'm not sure that there aren't some BUFFs at Diego also. There were some there for the Afghanistan festivities just over a year ago. Besides Jolly Old isn't all that far, if you can fly the great circle route, or nearly fly it. In fact, London is closer to Baghdad than Diego Garcia, 2540 miles vers 3345 miles. The great circule route appears to go over countries that would let us overfly, with the possible exception of Belgium, and a very small detour will allow flying over the Netherlands instead. Germany has granted overflight permission, IIRC, if not that would require a bigger job to the east.