nvubu,
Thanks, you are most kind.
They were all certainly seen as permanent airfields, or stations, and you have to remember that when these airfields were selected and designed, the standard RAF night bomber was the cloth covered biplane Handley Page Heyford, the more numerous light bomber was the equally cloth covered biplane Hawker Hart or Hind. The next generation was seen as the Fairey Hendon or Vickers Wellesley, the biggest thing on the horizon was the cloth covered Vickers Wellington, all capable of operating from the grass surfaces of the day. There was also a reluctance from both Air Ministry and Treasury to fund hard runways, especially as most senior staff officers of the time saw no need.
It is easy to criticise this with hindsight, but in the early to mid nineteen thirties when these places were designed, nobody foresaw the large 4 engine bomber or 1,000 bomber raids.
The reason why some never acquired hard runways is I suppose operational expediency. To build hard runways at these stations took time, and there was a reluctance to see too many out of service for up to a year while hard runways were constructed. Scampton for example was non operational for some considerable time as runways were built. The Dambusters raid took off from a grass covered Scampton. And as the war progressed places like Feltwell, Swanton Morley, Honington and Middle Wallop just never were slotted into a building programme.