I've discussed this at length on this and various other forums but a quick summary. The photos used by Google Earth et. al are from various sources, most notably a set compiled by Ordnance Survey post-war and sourced from censored pictures supplied by the RAF. Ordnance Survey used these photos to update their commercial publicly available maps. The airfield censorship depends on the year that the original RAF photo was taken and the source, for example RAF Grove has to top half of the airfield missing as that sortie was censored but a later one wasn't which shows the bottom. As you've spotted, airfields and facilities to be hidden are generally masked by clipping and photo retouching the area to show the features that existed pre-war. In the case of some HAA sites, they are simply obscured by convenient clouds. The Government even went as far as to change the policy of land use classification on OS maps. With the re-arming of Germany in the 30's, the government required OS to remove details of buildings and infrastructure of military sites and simply label them as "aerodrome". For new sites, they simply weren't added. In most cases, the classification colour of red was swapped for the less obvious pasture green. This went on into the 60's and even abandoned WWII airfields never showed any detail. You could write a book on the subject of map censorship to hide airfields.
