More likely to be sheer inertia in the supply chain. There's a war on, rapid production is essential, and minor modifications that don't really achieve anything useful (they might save a bit of time and a small amount of material over a long run but would stop production while drawings were amended and jigs adjusted) will simply accumulate until there's a major change that needs to happen, at which point all the modifications that are still applicable will be incorporated.
I can easily see a "Standard Wireless Table" being manufactured effectively unchanged for the whole of WW2.
Chris.