I have done the pre wash test on the fabrics I usually buy from my LQS. So far none of their fabrics have shrunk (except for one of their wide backs which they forewarned me about) while fabrics from other places which are also a little cheaper have shrunk considerably.
From my point of view it seems to depend on the quality of the fabric as to whether I do or don't.
I do pre wash and so on for swaps according to the rules but for myself not always
Maybe1day